0001962918-23-000044 | 10-Q | XBRL Viewer

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Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies There have been no changes to the significant accounting policies disclosed in Note 2 to the consolidated financial statements for the years ended December 31, 2022 and 2021 included in the Company’s final prospectus for the IPO (“Final Prospectus”) filed pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended (the “Securities Act”), with the U.S. Securities and Exchange Commission (the “SEC”) on May 5, 2023, except for performance-based restricted stock unit award. Basis of Presentation The condensed consolidated financial statements and accompanying notes are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. The accompanying financial statements are consolidated and include the accounts of ACELRYIN, INC. and its wholly owned subsidiary, WH2, LLC (the legal successor to ValenzaBio). The subsidiary has not had any operations or any balances from its inception. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2022 included in the Final Prospectus filed with the SEC on May 5, 2023. The information as of December 31, 2022, included in the condensed consolidated balance sheets was derived from the Company’s audited consolidated financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial statements. The results of operations for the nine months ended September 30, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023 or for any other interim period or for any other future year. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates estimates and assumptions, including but not limited to those related to the fair value of its derivative tranche liability, the fair value of its common stock, stock-based compensation expense, accruals for research and development expenses, valuation of deferred tax assets, and uncertain income tax positions. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates. Segment Information The Company has one operating segment. The Company’s focus is the research, development and commercialization of product candidates. The Company’s chief executive officer (“CEO”), who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America. Concentration of Credit Risk Cash and cash equivalents, and short-term marketable securities are financial instruments that potentially subject the Company to concentrations of credit risk. As of September 30, 2023, cash consists of cash deposited with one financial institution, and account balances exceed federally insured limits. The Company also has investments in money market funds, U.S. Treasury obligations, corporate debt obligations, and federal agency obligations, which can be subject to certain credit risks. The Company mitigates the risks by investing in high-grade financial instruments, limiting its exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its financial instruments. Leases The Company adopted ASU 2016-02, “Leases (Topic 842)” accounting standard as of January 1, 2022. The contractual arrangements that meet the definition of a lease are classified as operating or finance leases and are recorded on the balance sheets as both a right-of-use asset (“ROU asset”) and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company’s incremental borrowing rate (“IBR”). Lease ROU assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The Company currently does not have any finance leases. Operating lease ROU assets are adjusted for (i) payments made at or before the commencement date, (ii) initial direct costs incurred, and (iii) tenant incentives under the lease. As the implicit rate for the operating leases are not determinable, the Company determines its IBR based on the information available at the applicable lease commencement date. The IBR is determined by using the rate of interest that the Company would pay to borrow on a collateralized basis an amount equal to the lease payments for a similar term and in a similar economic environment where the asset is located. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably certain the Company will exercise any option to extend the contract. Lease costs for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Lease liabilities are increased by interest and reduced by payments each period, and the ROU asset is amortized over the lease term. Variable lease costs are recorded when incurred. In measuring the ROU assets and lease liabilities, the Company has elected to combine lease and non-lease components. The Company excludes short-term leases, if any, having initial terms of 12 months or less at lease commencement as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term for these types of leases. The Company did not have any leases as of and prior to January 1, 2023. Performance-Based Restricted Stock Unit Awards Performance-based restricted stock units (“PSUs”), awarded to employees vest upon the achievement of certain performance milestones and market conditions (i.e., specified average stock price hurdle) at the end of specified performance periods, subject to continuous service through each respective vest date. The amount of expense recognized is based on the grant date fair value of the PSU tranche corresponding to the performance condition of the tranche which is considered probable. The estimated grant date fair value of the market portion of the PSUs is based on a Monte Carlo simulation under each performance condition outcome. The Monte Carlo valuation model simulates the probabilities of stock price achievement, which requires management to make a number of assumptions including a 20-trading day volume-weighted average stock price, volatility of our peers, and the risk-free interest rate. Compensation expense for each tranche of a PSU award is recognized straight-line over the period commencing on the grant date of the award and ending on the vesting date of the tranche under the PSU award. Cumulative adjustments are recorded at each reporting date to reflect subsequent changes to the estimated outcome of the performance condition until the end of the respective performance period. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. The Company noted no recently issued accounting pronouncements that will impact its condensed consolidated financial statements. No new accounting pronouncements were adopted during the nine months ended September 30, 2023.

Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	20,726,850	48,458,034
Redeemable convertible preferred stock
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	0	40,743,522
Outstanding options to purchase common stock
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	8,704,462	5,036,946
Performance-based restricted stock units
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	2,988,492	0
Outstanding restricted stock units
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	2,183,413	1,107,213
ESPP Shares available for future grants
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	900,000	0
Shares available for future grants under Equity Incentive Plan
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	4,700,672	1,570,353
Options assumed upon ValenzaBio acquisition \| Outstanding options to purchase common stock
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	1,249,811	0

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Available-For-Sale Marketable Securities - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Allowance for credit loss	$ 0	$ 0	$ 0
Accrued interest receivable	700,000	700,000	$ 100,000
Accrued interest writeoff	$ 0	$ 0

Summary of Significant Accounting Policies (Details)	9 Months Ended
Summary of Significant Accounting Policies (Details)	Sep. 30, 2023 segment institution d
Accounting Policies [Abstract]
Number of operating segments \| segment	1
Number of financial institutions with cash deposits \| institution	1
Fair value assumptions, threshold trading days \| d	20

Fair Value Measurements

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The Company’s financial instruments measured at fair value on a recurring basis consist of Level 1, Level 2, and Level 3 financial instruments. Usually, marketable securities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. Corporate debt obligations, commercial paper, government agency obligations and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2.

Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. The Company had no Level 3 financial assets or liabilities as of September 30, 2023. The derivative tranche liability related to the Series C financing second tranche closing (Note 10) was a Level 3 financial liability as of December 31, 2022.

The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands):


	Fair Value Measurements as of September 30, 2023
As of September 30, 2023:	Total		Level 1		Level 2		Level 3

Assets:
Money market funds (included in cash and cash equivalents)	$	84,761	$	84,761	$	-	$	-
U.S. Treasury obligations ($223,032 included in cash and cash equivalents)	$	514,050	—		514,050		—
Corporate debt obligations ($46,714 included in cash and cash equivalents)	$	140,853	—		140,853		—
Federal agency obligations ($21,347 included in cash and cash equivalents)	$	41,891	—		41,891		—
Total fair value of assets	$	781,555	$	84,761	$	696,794	$	-


	Fair Value Measurements as of December 31, 2022
As of December 31, 2022:	Total		Level 1		Level 2		Level 3

Assets:
Money market funds (included in cash and cash equivalents)	$	238,223	$	238,223	$	-	$	-
U.S. Government bonds	25,459		-		25,459		-
U.S. Treasury bills	11,404		11,404		-		-
Corporate debt obligations	2,141		-		2,141		-
Federal agency obligations	8,506		-		8,506		-
Total fair value of assets	$	285,733	$	249,627	$	36,106	$	-

Liabilities:
Derivative tranche liability	$	10,291	$	-	$	-	$	10,291
Total fair value of liabilities	$	10,291	$	-	$	-	$	10,291


Classified as:	September 30, 2023		December 31, 2022
Cash and cash equivalents	$	374,862	$	238,223
Short-term marketable securities	406,693		47,510
Total cash equivalents and marketable securities	$	781,555	$	285,733

The following table sets forth the changes in the fair value of Level 3 liabilities (in thousands):


	Derivative Tranche Liability
Balance as of December 31, 2022	$	10,291
Change in fair value	(10,291)
Balance as of September 30, 2023	$	—

The derivative tranche liability was issued on September 9, 2022 with a fair value of $10.8 million. The fair value of the derivative tranche liability has been estimated using a probability weighted model. Upon the closing of the IPO, on May 9, 2023, the derivative tranche liability was remeasured at fair value based on its intrinsic value and it was terminated. Intrinsic value was calculated as a difference between the IPO price of $18.00 per share and $12.2661, the Series C second tranche closing per share purchase price. The fair value of the derivative tranche liability upon the closing of the IPO was determined to be zero and the Series C Second Tranche Closing was terminated. The following significant assumptions were used to estimate fair value of the derivative tranche liability as of December 31, 2022:


	December 31, 2022
Probability of achieving specified conditions	80		%
Fair value of Series C preferred stock share	$	12.2661
Discount rate	25		%

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Redeemable Convertible Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Shares Authorized (in shares)	0			104,461,636
Shares Issued (in shares)	0			40,743,522
Shares Outstanding (in shares)	0	0	40,743,522	40,743,522	40,743,522	28,514,641	28,514,641	16,285,718
Aggregate Liquidation Preference				$ 408,000
Net Carrying Value	$ 0	$ 0	$ 396,593	$ 396,593	$ 396,592	$ 257,594	$ 257,594	$ 132,620
Series A redeemable convertible preferred stock
Class of Stock [Line Items]
Shares Authorized (in shares)				8,000,000
Shares Issued (in shares)				4,056,795
Shares Outstanding (in shares)				4,056,795
Aggregate Liquidation Preference				$ 8,000
Net Carrying Value				$ 7,916
Series B redeemable convertible preferred stock
Class of Stock [Line Items]
Shares Authorized (in shares)				48,230,900
Shares Issued (in shares)				24,457,846
Shares Outstanding (in shares)				24,457,846
Aggregate Liquidation Preference				$ 250,000
Net Carrying Value				$ 249,678
Series C redeemable convertible preferred stock
Class of Stock [Line Items]
Shares Authorized (in shares)				48,230,736
Shares Issued (in shares)				12,228,881
Shares Outstanding (in shares)				12,228,881
Aggregate Liquidation Preference				$ 150,000
Net Carrying Value				$ 138,999

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

- Definition

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

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+ Details

Description of Business, Organization and Liquidity	9 Months Ended
Description of Business, Organization and Liquidity	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business, Organization and Liquidity	Description of Business, Organization and Liquidity Organization and Business ACELYRIN, INC. (the “Company”) is a late-stage clinical biopharma company focused on identifying, acquiring, and accelerating the development and commercialization of transformative medicines. The Company was incorporated in the State of Delaware on July 27, 2020. Since its inception, the Company has devoted substantially all of its resources to organizing the Company, hiring personnel, business planning, acquiring and developing its product candidates, performing research and development, enabling manufacturing activities in support of its product development efforts, establishing and protecting its intellectual property portfolio, raising capital, and providing general and administrative support for these activities. The Company did not have any significant operations from the inception date until August 2021. On August 9, 2021, the Company entered into the License and Collaboration Agreement with Affibody AB, a Swedish company, and licensed worldwide development, manufacturing and commercialization rights to a therapeutic candidate, izokibep, for use in the treatment of inflammatory and autoimmune disorders, excluding rights in certain Asian and Nordic countries. See Note 7 for further details. On January 4, 2023, the Company closed the acquisition of ValenzaBio, Inc. (“ValenzaBio”) and issued as consideration 18,885,731 shares of its Class A common stock (“Class A Common Stock”). ValenzaBio was a privately held company developing therapies for autoimmune and inflammatory diseases. The ValenzaBio acquisition added additional assets to the Company’s portfolio, including lonigutamab and SLRN-517. See Note 3 for further details. Reverse Stock Split In April 2023, the Company effected a reverse split of shares of the Company’s outstanding common stock and redeemable convertible preferred stock at a ratio 1.972-for-1 (the “Reverse Stock Split”). The number of authorized shares and par value per share were not adjusted as a result of the Reverse Stock Split. All references to shares, restricted stock units (“RSUs”) and restricted stock awards (“RSAs”), options to purchase common stock, share data, per share data, and related information contained in the condensed consolidated financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented. Initial Public Offering On May 4, 2023, the Company’s Form S-1 Registration Statement for its initial public offering (the “IPO”) was declared effective, and on May 9, 2023, the Company closed its IPO and issued 34,500,000 shares of common stock at a price to the public of $18.00 per share, including 4,500,000 shares issued upon the exercise of underwriters’ option to purchase additional shares of common stock. The Company received gross proceeds of $621.0 million. Net proceeds were approximately $573.6 million, after deducting underwriting discounts and commissions and offering costs of $47.4 million. The common stock began trading on the Nasdaq Global Select Market on May 5, 2023, under the symbol “SLRN”. Immediately prior to the IPO closing, each share of the Company’s redeemable convertible preferred stock then outstanding converted into an equivalent number of shares of Class A Common Stock, and thereafter each share of Class A Common Stock then issued and outstanding was reclassified and became one share of the Company’s common stock. Liquidity The Company has incurred significant losses and negative cash flows from operations since its inception. During the nine months ended September 30, 2023 and 2022, the Company incurred net losses of $286.4 million and $45.0 million, respectively. The net loss of $286.4 million in the nine months ended September 30, 2023 includes $123.1 million of expenses related to acquired in-process research and development assets without alternative future use and $10.0 million license fee payment to Pierre Fabre incurred in connection with the ValenzaBio acquisition. As of September 30, 2023, the Company had an accumulated deficit of $393.5 million. Cash used in operating activities was $96.1 million and $43.4 million for the nine months ended September 30, 2023 and 2022, respectively. The Company has historically financed its operations primarily through the sale of shares of its redeemable convertible preferred stock in private placements and the sale of shares of its common stock in its IPO. As of September 30, 2023, the Company had cash and cash equivalents and short-term marketable securities of $788.4 million. The Company does not have any products approved for sale and has not generated any revenue from product sales to date. The Company expects to continue to incur significant and increasing expenses and substantial losses for the foreseeable future as it continues its development of and seeks regulatory approvals for its product candidates and commercializes any approved products, seeks to expand its product pipeline and invests in its organization. The Company’s ability to achieve and sustain profitability will depend on its ability to successfully develop, obtain regulatory approval for and commercialize its product candidates. There can be no assurance that the Company will ever earn revenue or achieve profitability, or if achieved, that the revenue or profitability will be sustained on a continuing basis. Unless and until it does, the Company will need to continue to raise additional capital. Management expects that its cash and cash equivalents and short-term marketable securities will be sufficient to fund its current operating plan and capital expenditure requirements for at least the next 12 months from the date of issuance of these condensed consolidated financial statements.

ValenzaBio Acquisition - Schedule of Total Purchase Consideration (Details) - ValenzaBio Asset Acquisition	Jan. 04, 2023 USD ($) $ / shares shares
Asset Acquisition [Line Items]
Issued common stock	$ 128,735,000
Transaction costs	1,271,000
Cash	7,663
Total	$ 130,014,000
Shares issued (in dollars per share) \| $ / shares	$ 6.86
Shares issued (in shares) \| shares	2,013,673
Contingent consideration	$ 100,000

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2022	Mar. 31, 2022
Statement of Stockholders' Equity [Abstract]
Issuance of redeemable convertible preferred stock, derivative liability	$ 10,778
Issuance of redeemable convertible preferred stock, issuance costs	$ 223	$ 26

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

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+ Details

Related Party Transactions (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Related Party Transaction [Line Items]
Payments of stock issuance costs	$ 0	$ 138
Related Party
Related Party Transaction [Line Items]
Payments of stock issuance costs		$ 10

Redeemable Convertible Preferred Stock - Narrative (Details)			1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2023 $ / shares shares	May 09, 2023 $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Feb. 28, 2022 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) shares	Sep. 30, 2023 USD ($) director	Sep. 30, 2022 USD ($) $ / shares	Dec. 31, 2022	Oct. 31, 2020 $ / shares
Class of Stock [Line Items]
Issuance of convertible preferred stock (in shares) \| shares					12,228,881	12,228,923
Shares issued, gross cash proceeds					$ 138,998,000	$ 124,974,000
Temporary equity, convertible, conversion ratio		100.00%					100.00%		1.00%
Temporary equity, voting rights, number of directors \| director							3
Series B redeemable convertible preferred stock
Class of Stock [Line Items]
Issuance of convertible preferred stock (in shares) \| shares				12,228,923
Shares issued, price per share (in dollars per share) \| $ / shares				$ 10.2217
Shares issued, gross cash proceeds				$ 125,000,000
Stock issuance costs				$ 100,000
Dividend rate							8.00%
Dividends payable							$ 0	$ 0
Series C redeemable convertible preferred stock
Class of Stock [Line Items]
Issuance of convertible preferred stock (in shares) \| shares	12,228,881	12,228,881	12,228,881
Shares issued, price per share (in dollars per share) \| $ / shares	$ 12.2661	$ 12.2661	$ 12.2661		$ 12.2661			$ 12.2661
Shares issued, gross cash proceeds			$ 150,000,000
Stock issuance costs			$ 200,000
Temporary equity, convertible, conversion ratio	1000.00%
Dividend rate							8.00%
Dividends payable							$ 0	$ 0
Series A redeemable convertible preferred stock
Class of Stock [Line Items]
Shares issued, price per share (in dollars per share) \| $ / shares										$ 1.9720
Dividend rate							8.00%
Dividends payable							$ 0	$ 0

ValenzaBio Acquisition

9 Months Ended

Sep. 30, 2023

Business Combination and Asset Acquisition [Abstract]

ValenzaBio Acquisition

On December 20, 2022, the Company entered into the Agreement and the Plan of Merger and Reorganization (the “Merger Agreement”) to acquire ValenzaBio. In connection with the planned ValenzaBio acquisition, the Company formed two wholly owned subsidiaries, WH1, Inc. and WH2 LLC in November 2022. Through the two-step merger and restructuring, WH1 Inc. was merged with and into ValenzaBio with WH1 Inc. ceasing to exist, and ValenzaBio was then merged with and into WH2 LLC, with WH2 LLC continuing as the legal successor to ValenzaBio. (the “Acquisition”). The Acquisition closed on January 4, 2023 (the “Closing Date”), and is anticipated to qualify as a tax-free reorganization for U.S. federal income tax purposes.

The Company concluded that the Acquisition is an asset acquisition as substantially all of the fair value of the gross assets acquired, excluding cash, was concentrated in a single asset, lonigutamab, and the Company did not acquire a workforce or any substantive process capable of significantly contributing to the ability to create outputs.

As consideration, the Company issued 18,885,731 shares of its Class A Common Stock to ValenzaBio stockholders, of which 2,013,673 are being held by Seller LLC for any post-acquisition costs and general indemnities for 12 months from the Closing Date (“Holdback Release Date”), and paid $7,663 in cash to one non-accredited investor. Additionally, $0.1 million is payable in cash to Seller LLC to cover Seller LLC’s fees and expenses related to the Acquisition, with any unused amount to be released to ValenzaBio stockholders as soon as practicable following the completion of Seller LLC’s responsibilities. The Company also incurred $1.2 million of acquisition-related costs that were included in the total consideration and capitalized to assets acquired.

The Company assumed options of certain ValenzaBio option holders who entered into consulting agreements with the Company, which became options for the purchase of an aggregate of 1,249,811 shares of the Company’s Class A Common Stock upon the closing of the Acquisition on January 4, 2023. The assumed options vested in full on March 31, 2023. Each assumed option is exercisable until the earlier of (i) 12 months following the termination of the option holder’s continuous service with the Company, or (ii) the original expiration date of such assumed option.

Outstanding ValenzaBio shares were exchanged into shares of the Company’s Class A Common Stock and the options described above assumed at an exchange ratio of 0.8027010-for-one.

The following table represents the total purchase consideration (in thousands):


Issued Class A Common Stock (1)	$	128,735
Transaction costs (2)	1,271
Cash (3)	8
Total	$	130,014

(1)Shares were issued for consideration at $6.86 per share, including 2,013,673 shares that are being held by Seller LLC until the Holdback Release Date. The Company used a third party valuation specialist to assist management in determining the fair value of the shares of Class A Common Stock at the Closing Date.

(2)Legal and advisory transaction costs of $1.3 million incurred by the Company in connection with the Acquisition, including $0.1 million payable in cash to Seller LLC for the expense fund.

(3)Cash payment of $7,663 to one non-accredited investor for settlement of vested ValenzaBio options.

The following is the allocation of the purchase consideration to the acquired assets and liabilities (in thousands):


Cash	$	11,369
Prepaid expenses and other current assets	2,074
In-process research and development assets	123,057
Accounts payable	(1,628)
Accrued research and development expenses	(4,805)
Accrued compensation and other current liabilities	(53)
Total net asset acquired	$	130,014

In-process research and development (“IPR&D) assets were related to acquired product candidates: lonigutamab in clinical trials and SLRN-517 in preclinical development. The fair value of in-process research and development assets was based on the present value of future discounted cash flows, which was based on significant estimates. These estimates included the number of potential patients and market prices of future product candidates, costs required to conduct clinical trials, future milestones and royalties payable under acquired license agreements, costs to receive regulatory approval and potentially commercialize product candidates, as well as estimates for probability of success and the discount rate. The estimated fair values of lonigutamab and SLRN-517 assets were $114.8 million and $8.2 million, respectively. The Company concluded that acquired assets do not have an alternative future use and recognized the full amount of $123.1 million as research and development expenses in the condensed consolidated statement of operations and comprehensive loss in January 2023.

There are a number of additional obligations under the Merger Agreement that are separate from the assets and liabilities acquired, including the following:

Assumed options. The assumed options, discussed above, did not have substantive service requirement, and were accounted as a separate transaction from the Acquisition. The fair values of assumed options of $3.1 million and $1.8 million was expensed as research and development and general and administrative expenses, respectively, in the condensed consolidated statement of operations and comprehensive loss for the three months ended March 31,2023.

Settled equity awards. In accordance with the severance obligations of ValenzaBio and per the terms of the Merger Agreement, certain unvested options and restricted stock awards of former ValenzaBio employees, who did not enter into consulting agreements with the Company, were accelerated and net exercised upon the closing of the Acquisition and termination of employment of such ValenzaBio employees. The fair value of unvested equity awards of $0.9 million was expensed as general and administrative expense in the condensed consolidated statement of operations and comprehensive loss for the three months ended March 31, 2023. Payments in cash to one non-accredited investor for settlement of unvested ValenzaBio options and one former ValenzaBio employee to whom options were promised but not granted at the Closing Date of $8,387 and $30,000, respectively, were expensed as general and administrative expenses in the condensed consolidated statement of operations and comprehensive loss for the three months ended March 31, 2023.

Severance payment obligation. In accordance with the severance plan of ValenzaBio, the Company is obligated to make severance payments to certain former ValenzaBio employees of approximately $5.1 million, including estimated taxes, for a period of three to 18 months from the Closing Date, depending on the position and tenure of such employees with ValenzaBio. The Company recognized the estimated fair value of severance payments obligations of $2.5 million and $2.4 million at the Closing Date as research and development and general and administrative expenses, respectively, in the condensed consolidated statement of operations and comprehensive loss for the three months ended March 31, 2023. The fair value of severance payments obligations was estimated based on future expected cash flows discounted to the Closing Date and a discount rate of 8%. The Company will accrete the fair value of severance payments obligations to the amounts payable over the obligation period as either research and development or general and administrative expenses based on the former employees’ functional department.

As of September 30, 2023, severance payments obligations to ValenzaBio employees in the amount of $1.2 million were included in the condensed consolidated balance sheet. The accretion of severance payments obligations of less than

$0.1 million and less than $0.1 million were included in research and development and general and administrative expenses, respectively, in the condensed consolidated statement of operations and comprehensive loss for the nine months ended September 30, 2023. The accretion of severance payments obligations was less than $0.1 million for the three months ended September 30, 2023.Amendment to Pierre Fabre Agreement. The Company, ValenzaBio and Pierre Fabre Medicament SAS (“Pierre Fabre”) entered into an amendment to the license and commercialization agreement, which became effective on the Closing Date. The Company paid a $10.0 million non-refundable license fee to Pierre Fabre. See Note 7 for additional details.

Available-For-Sale Marketable Securities

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Available-For-Sale Marketable Securities

The following tables summarize the estimated fair value of the Company’s available-for-sale marketable securities as of September 30, 2023 and December 31, 2022 (in thousands):


As of September 30, 2023:	Total Amortized Cost		Total Unrealized Gains		Total Unrealized Loss		Total Estimated Fair Value

Money market funds (included in cash and cash equivalents)	$	84,761	$	-	$	-	$	84,761
U.S. Treasury obligations ($223,032 included in cash and cash equivalents)	514,029		51		(30)		514,050
Corporate debt obligations ($46,714 included in cash and cash equivalents)	140,923		4		(74)		140,853
Federal agency obligations ($21,347 included in cash and cash equivalents)	41,892		5		(6)		41,891
Total available for sale marketable securities	$	781,605	$	60	$	(110)	$	781,555


As of December 31, 2022:	Total Amortized Cost		Total Unrealized Loss (1)		Total Estimated Fair Value

Money market funds (included in cash and cash equivalents)	$	238,223	$	-	$	238,223
U.S. Government bonds	25,506		(47)		25,459
U.S. Treasury obligations	11,430		(26)		11,404
Corporate debt obligations	2,145		(4)		2,141
Federal agency obligations	8,515		(9)		8,506
Total available for sale marketable securities	$	285,819	$	(86)	$	285,733

(1)The Company did not have any gross unrealized gains as of December 31, 2022.

As of September 30, 2023 and December 31, 2022, no significant facts or circumstances were present to indicate a deterioration in the creditworthiness of the issuers of the Company’s marketable securities, and the Company has no requirement or intention to sell these securities before maturity or recovery of their amortized cost basis. The Company considered the current and expected future economic and market conditions and determined that its investments were not significantly impacted by such conditions. For all securities with a fair value less than its amortized cost basis, the Company determined the decline in fair value below amortized cost basis to be immaterial and non-credit related, and therefore no allowance for losses has been recorded. During the nine months ended September 30, 2023 and for the year ended December 31, 2022, the Company did not recognize any impairment losses on its investments.

The Company presents accrued interest receivable related to the available-for-sale marketable securities in prepaid expenses and other current assets, separate from short-term investments in the condensed consolidated balance sheet. As of each of September 30, 2023 and December 31, 2022, accrued interest receivable was $0.7 million and $0.1 million, respectively. The Company’s accounting policy is to not measure an allowance for credit losses for accrued interest receivables and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which it considers to be in the period in which the Company determines the accrued interest will not be collected. The Company has not written off any accrued interest receivables for the three and nine months ended September 30, 2023.

Income Taxes (Details)	9 Months Ended
Income Taxes (Details)	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Valuation allowance, minimum	100.00%
Effective income tax rate	0.00%

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	0	104,461,636
Redeemable convertible preferred stock, issued (in shares)	0	40,743,522
Redeemable convertible preferred stock, outstanding (in shares)	0	40,743,522
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.00001
Redeemable convertible preferred stock, aggregate liquidation preference		$ 408,000
Preferred stock, authorized (in shares)	10,000,000	0
Preferred stock, par value (in dollars per share)	$ 0.00001
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, authorized (in shares)	790,000,000	229,461,636
Common stock, issued (in shares)	97,240,419	97,240,419
Common stock, outstanding (in shares)	2,767,359	2,767,359

Consolidated Balance Sheet Components (Tables)

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure

Prepaid expenses and other current assets consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Prepaid insurance and other current assets	$	1,834	$	86
Prepaid research and development expenses	1,645		682
VAT receivable	1,292		—
Prepaid other services	776		288
Interest receivable	660		138
Research and development credit receivable	-		250
Total	$	6,207	$	1,444

Other non-current assets consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Prepaid research and development expenses, non-current	$	2,448	$	1,964
Security deposits	34		—
Deferred IPO offering costs	—		774
Acquisition transaction costs	-		1,121
Total	$	2,482	$	3,859

Property, Plant and Equipment

Property, plant and equipment consisted of the following as of September 30, 2023 (in thousands):


	September 30, 2023
Construction in progress	$	1,499
Furniture and fixtures	263
Computer and other equipment	344
Leasehold improvements	90
Total property, plant and equipment, gross	2,196
Less: accumulated depreciation and amortization	(67)
Property, plant and equipment, net	$	2,129

Other Current Liabilities

Accrued compensation and other current liabilities consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued compensation	$	4,016	$	3,068
Accrued professional services fees (1)	751		808
Other accrued expenses and current liabilities	377		361
Total	$	5,144	$	4,237

(1)IPO offering costs included in accrued liabilities were zero and $0.2 million as of September 30, 2023 and December 31, 2022, respectively.

Common Stock (Tables)

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Schedule of Common Stock Reserved for Future Issuance

As of September 30, 2023 and December 31, 2022, the Company’s common stock reserved for future issuance was as follows:


	September 30,	December 31,
	2023	2022
Shares available for future grants under Equity Incentive Plan	4,700,672	1,570,353
Outstanding stock options	8,704,462	5,036,946
Performance-based restricted stock units	2,988,492	-
Outstanding restricted stock units	2,183,413	1,107,213
Options assumed upon ValenzaBio acquisition	1,249,811	—
ESPP Shares available for future grants	900,000	—
Redeemable convertible preferred stock	—	40,743,522
Total shares reserved for future issuance	20,726,850	48,458,034

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (286,429)	$ (44,965)
Adjustments to reconcile net loss to net cash used in operations:
Expense related to acquired in-process research and development assets	133,057	0
Stock-based compensation expense	30,953	2,539
Net amortization of premiums and accretion of discounts on marketable securities	(5,564)	78
Change in fair value of derivative tranche liability	(10,291)	0
Depreciation and amortization expense	67	0
Non-cash lease expense	108	0
Changes in assets and liabilities:
Prepaid expense and other current assets	(3,323)	(2,592)
Prepaid expenses and other assets, non-current	1,724	(1,172)
Accounts payable	11,225	1,167
Accrued research and development expenses	30,773	644
Accrued compensation and other current liabilities	2	873
Operating lease liability	(96)	0
Severance liability	1,720	0
Net cash used in operating activities	(96,074)	(43,428)
Cash flows from investing activities
ValenzaBio assets acquisition, cash acquired net of acquisition costs	10,007	0
Cash paid to acquire in-process research and development assets	(10,000)	0
Purchase of marketable securities	(537,987)	(262,005)
Proceeds from maturities of short-term marketable securities	128,728	152,518
Sales of marketable securities	56,310	0
Purchase of property, plant and equipment	(2,196)	0
Net cash used in investing activities	(355,138)	(109,487)
Cash flows from financing activities
Issuance of common stock upon initial public offering, net of commissions and issuance costs	574,134	0
Proceeds from exercise of common stock options	31
Proceeds from the issuance of redeemable convertible preferred stock, net of issuance costs	0	263,973
Proceeds allocated to the derivative tranche liability	0	10,778
Payments for deferred offering costs	0	(138)
Taxes paid related to net share settlement of restricted stock units	(8,325)	0
Net cash provided by financing activities	565,840	274,613
Net increase in cash and cash equivalents	114,628	121,698
Cash and cash equivalents at beginning of period	267,110	102,242
Cash and cash equivalent at end of period	381,738	223,940
Supplemental disclosure of cash flow information:
Conversion of 40,743,522 redeemable convertible preferred stock upon the closing of initial public offering	396,593	0
Common stock issued in connection with ValenzaBio acquisition	128,735	0
Right-of-use assets obtained in exchange for operating lease liability	$ 1,348	$ 0

Commitments and Contingent Liabilities

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

License Agreements

The Company is required to pay certain milestones upon the achievement of specific development and regulatory events, upon products’ commercialization and products’ royalties under its license agreements, including its agreements with Affibody, Pierre Fabre, Novelty Nobility and other non-exclusive license agreements. None of the milestones were achieved or probable, all products were in development, as such, no milestones or royalties were accrued in the condensed consolidated balance sheets as of September 30, 2023 and December 31, 2022.

Research and Development Agreements

The Company enters into various agreements in the ordinary course of business, such as those with suppliers, contract research organizations, contract manufacturing organizations, and clinical trial sites. These contracts generally provide for termination on notice or may have a potential termination fee if a purchase order is canceled within a specified time. As of September 30, 2023, and December 31, 2022, there were no amounts accrued related to termination and cancellation charges in the consolidated balance sheets, as the Company has not determined cancellation to be probable.

Lease

In January 2023, the Company entered into a lease agreement to rent approximately 10,012 square feet of office space in Agoura Hills, California. The term of the lease is 65 months with an option to extend it for an additional three years. Monthly rent payments are approximately $30,500, subject to an annual 3.0% increase and six months rental abatement during the first year. In addition to the base rent, the Company is obligated to pay variable costs related to its share of operating expenses and taxes. In connection with the lease agreement, the Company made a security deposit of $34,000, that is included in prepaid expenses and other assets, non-current in the condensed consolidated balance sheet as of September 30, 2023.

As of the lease commencement date the Company recorded $1.3 million as right-of-use (“ROU”) asset and operating lease liability, non-current, in the condensed consolidated balance sheet.

In July 2023, the Company entered into a lease agreement to rent approximately 22,365 square feet of office space in South San Francisco with the commencement date to be determined upon completion of work to be performed by the landlord. The term of the lease is 60 months with an option to extend it for an additional three years at then current market rates. Monthly base rent payments are approximately $150,000, subject to an annual 3.5% increase and a share of building operating expenses. The lease has not commenced as of September 30, 2023.

Operating lease costs were less than $0.1 million and $0.2 million for the three and nine months ended September 30, 2023, respectively, and were recorded in general and administrative expenses and research and development expenses in the condensed consolidated statements of operations and comprehensive loss.

The following table summarizes a maturity analysis of the Company’s operating lease liabilities showing the aggregate lease payments as of September 30, 2023 (in thousands):


2023 (remainder of the year)	$	61
2024	375
2025	386
2026	398
2027	409
Thereafter	280
Total future lease payments	1,909
Less imputed interest	(476)
Total operating lease liability balance	1,433
Less current portion of lease liability (included in Accrued compensation and other current liabilities)	(181)
Operating lease liability, non-current	$	1,252

The weighted-average remaining lease term was 59 months and the weighted-average discount rate was 12%.

Cash paid for amounts included in the measurement of lease liabilities was less than $0.1 million.

Legal Contingencies

From time to time, the Company may become involved in legal proceedings arising from the ordinary course of business. The Company records a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount. Management is not aware of any legal matters that could have a material adverse effect on the Company’s financial position, results of operations or cash flows.

Guarantees and Indemnifications

In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. Its exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at a request in such capacity. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of September 30, 2023, the Company did not have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

Commitments and Contingent Liabilities (Tables)

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

Lessee, Operating Lease, Liability, to be Paid, Maturity

The following table summarizes a maturity analysis of the Company’s operating lease liabilities showing the aggregate lease payments as of September 30, 2023 (in thousands):


2023 (remainder of the year)	$	61
2024	375
2025	386
2026	398
2027	409
Thereafter	280
Total future lease payments	1,909
Less imputed interest	(476)
Total operating lease liability balance	1,433
Less current portion of lease liability (included in Accrued compensation and other current liabilities)	(181)
Operating lease liability, non-current	$	1,252

Equity Incentive Plan (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

A summary of option activity under the 2020 Plan and 2023 Plan is as follows:


	Number of Options	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022	5,036,946	$	4.7872	9.5	$	5,488
Options granted	4,771,615	$	16.8645
Options exercised	(40,570)	0.7700
Options forfeited	(1,063,529)	10.9236
Outstanding at September 30, 2023	8,704,462	$	10.6860	8.9	$	26,543
Exercisable at September 30, 2023	1,347,153	$	4.3478	6.7	$	8,028
Vested and expected to vest at September 30, 2023	8,704,462	$	10.6860	8.9	$	26,543

Summary of Performance Share Activity

A summary of PSU activity based on the target number of shares is presented in the following table:


	Number of PSUs	Weighted-Average Grant Date Fair Value*
Outstanding at December 31, 2022	—	$	—
Granted	3,135,104	$	27.43
Vested	—	$	—
Forfeited	(146,612)	$	27.43
Outstanding at September 30, 2023	2,988,492	$	27.43

*The grant date fair value is based only on the PSUs with market conditions and does not factor in any performance conditions.

Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions

The Company uses the Black-Scholes valuation model and made the following assumptions to estimate fair value of each option at the grant date for the three and nine months ended September 30, 2023 and 2022:


	Three Months Ended September 30,	Three Months Ended September 30,	Nine Months Ended September 30,	Nine Months Ended September 30,
	2023	2022	2023	2022

Expected volatility	87.34% - 87.93%	99.91%	75.30% - 92.20%	99.99% - 102.81%
Expected dividend yield	0%	0%	0%	0%
Expected term (in years)	5.95 – 6.04 years	6.08 years	5.77 - 6.08 years	5.90 - 6.08 years
Risk-free interest rate	4.14% - 4.61%	3.05%	3.30% - 4.61%	1.69% - 3.26%

Share-Based Payment Arrangement, Expensed and Capitalized, Amount

The following table presents the classification of stock-based compensation expense related to awards granted under its equity incentive plans (in thousands):


	Three Months ended September 30,				Nine Months ended September 30,
	2023		2022		2023		2022
General and administrative expenses	$	11,741	$	196	$	22,292	$	1,677
Research and development expenses	3,572		364		8,661		862
Total stock-based compensation expense	$	15,313	$	560	$	30,953	$	2,539

The stock-based compensation expense relates to the following equity-based awards:


	Three Months ended September 30,				Nine Months ended September 30,
	2023		2022		2023		2022
Restricted stock units	$	2,345	$	—	$	7,884	$	—
Performance-based restricted stock units	4,265		—		4,265		—
Stock options	8,577		560		18,661		1,234
ESPP	126		—		143		—
Restricted stock awards	—		—		—		1,305
Total stock-based compensation expense	$	15,313	$	560	$	30,953	$	2,539

Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2023	Nov. 06, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-41696
Entity Registrant Name	ACELYRIN, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-2406735
Entity Address, Address Line One	4149 Liberty Canyon Road
Entity Address, City or Town	Agoura Hills
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91301
City Area Code	805
Local Phone Number	730-0360
Title of 12(b) Security	Common Stock ($0.00001 par value)
Trading Symbol	SLRN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		97,339,494
Entity Central Index Key	0001962918
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Amendment Flag	false

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesFor the three and nine months ended September 30, 2023 and 2022, the Company did not record an income tax provision. The Company continues to maintain a 100% valuation allowance on total deferred tax assets. The Company believes it is more likely than not that the related deferred tax asset will not be realized. As a result, the Company’s effective tax rate will remain at 0% because there are no estimated or discrete items that would impact the tax provision.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

ValenzaBio Acquisition - Narrative (Details)		3 Months Ended			9 Months Ended
ValenzaBio Acquisition - Narrative (Details)	Jan. 04, 2023 USD ($) shares	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets					$ 133,057,000	$ 0
Research and development		$ 74,562,000		$ 12,509,000	272,512,000	38,222,000
Severance payable, current		1,200,000			1,200,000
Payments to acquire in-process research and development					10,000,000	$ 0
Minimum
Asset Acquisition [Line Items]
Severance payment obligation period	3 months
Maximum
Asset Acquisition [Line Items]
Severance payment obligation period	18 months
Unvested Equity Awards
Asset Acquisition [Line Items]
Separately recognized expenses			$ 900,000
Severance Payment Obligation
Asset Acquisition [Line Items]
Liabilities recognized	$ 5,100,000
Severance Payment Obligation \| Discount rate
Asset Acquisition [Line Items]
Measurement input	8.00%
Research and Development Expense \| Assumed Options
Asset Acquisition [Line Items]
Separately recognized expenses			3,100,000
Research and Development Expense \| Severance Payment Obligation
Asset Acquisition [Line Items]
Separately recognized expenses			2,500,000
Research and Development Expense \| Severance Payment Obligation Accretion
Asset Acquisition [Line Items]
Separately recognized expenses		$ 100,000			100,000
General and Administrative Expense \| Assumed Options
Asset Acquisition [Line Items]
Separately recognized expenses			1,800,000
General and Administrative Expense \| Severance Payment Obligation
Asset Acquisition [Line Items]
Separately recognized expenses			2,400,000
General and Administrative Expense \| Severance Payment Obligation Accretion
Asset Acquisition [Line Items]
Separately recognized expenses					100,000
Non-Accredited Investor \| General and Administrative Expense
Asset Acquisition [Line Items]
Separately recognized expenses			8,387
Former ValenzaBio Employee \| General and Administrative Expense
Asset Acquisition [Line Items]
Separately recognized expenses			$ 30,000
Pierre Fabre
Asset Acquisition [Line Items]
Payments to acquire in-process research and development	$ 10,000,000				10,000,000.0
ValenzaBio Asset Acquisition
Asset Acquisition [Line Items]
Shares issued (in shares) \| shares	2,013,673
Shares issued, withholding period	12 months
Asset acquisition payment	$ 7,663
Contingent consideration	100,000
Transaction cost, net	$ 1,200,000
Options exercisable (in shares) \| shares	1,249,811
Option exercisable period	12 months
Options exchange ratio	0.008027010
Research and development	$ 123,100,000				$ 123,100,000
ValenzaBio Asset Acquisition \| Common Class A
Asset Acquisition [Line Items]
Shares issued (in shares) \| shares	18,885,731
ValenzaBio Asset Acquisition \| lonigutamab
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets	$ 114,800,000
ValenzaBio Asset Acquisition \| SLRN-517
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets	$ 8,200,000

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (83,940)	$ (26,039)	$ (176,450)	$ (14,406)	$ (14,474)	$ (16,085)	$ (286,429)	$ (44,965)
Denominator:
Weighted average common shares outstanding (in shares)	97,227,070			3,358,972			61,580,296	3,268,666
Less: Weighted-average common shares subject to repurchase (in shares)	(354,323)			(1,594,679)			(442,191)	(1,848,467)
Weighted-average common shares outstanding, basic (in shares)	96,872,747			1,764,293			61,138,105	1,420,199
Weighted-average common shares outstanding, diluted (in shares)	96,872,747			1,764,293			61,138,105	1,420,199
Net loss per share attributable to common stockholder, basic (in shares)	$ (0.87)			$ (8.17)			$ (4.68)	$ (31.66)
Net loss per share attributable to common stockholder, diluted (in shares)	$ (0.87)			$ (8.17)			$ (4.68)	$ (31.66)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 7
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-URI https://asc.fasb.org//1943274/2147482689/260-10-45-7

+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Redeemable Convertible Preferred Stock

9 Months Ended

Sep. 30, 2023

Temporary Equity [Abstract]

Redeemable Convertible Preferred Stock

In February 2022, the Company closed the Series B Second Tranche financing and issued 12,228,923 shares of Series B redeemable convertible preferred stock (the “Series B Stock”) at a price of $10.2217 per share for gross cash proceeds of $125.0 million and incurred less than $0.1 million issuance costs.

In September 2022, the Company entered into a Series C stock purchase agreement and issued 12,228,881 shares of Series C redeemable convertible preferred stock (the “Series C Stock”) at a price of $12.2661 per share for gross cash proceeds of $150.0 million (the “Series C First Tranche Closing”) and incurred issuance costs of $0.2 million.

Pursuant to the Series C preferred stock purchase agreement, the Company and investors agreed to issue and purchase an additional 12,228,881 shares of Series C Stock at the same purchase price of $12.2661 per share on June 30, 2023, subject to meeting certain conditions (the “Series C Second Tranche Closing”) (see Note 10). If a Series C Stock holder did not purchase the full number of the Series C Second Tranche shares that was required to be purchased by it on the Series C Second Tranche Closing date and this holder became a defaulting purchaser, then each 10 shares of Series C Stock held by such holder would have automatically converted into one share of Class A Common Stock, as adjusted for any stock dividends, splits, recapitalizations and the like in accordance with the Company’s then-current certificate of incorporation.

On May 9, 2023, the IPO closing date, each share of the Company’s redeemable convertible preferred stock then issued and outstanding automatically converted into one share of the Company’s Class A Common Stock, thereafter each share of Class A Common Stock then issued and outstanding was reclassified and became one share of common stock and the Series C Second Tranche Closing was terminated.

The authorized, issued, and outstanding shares of the Company’s convertible preferred stock and liquidation preferences as of December 31, 2022 were as follows (in thousands, except for share amounts):


	Shares Authorized	Shares Issued and Outstanding	Aggregate Liquidation Preference		Net Carrying Value
Series A redeemable convertible preferred stock	8,000,000	4,056,795	$	8,000	$	7,916
Series B redeemable convertible preferred stock	48,230,900	24,457,846	250,000		249,678
Series C redeemable convertible preferred stock	48,230,736	12,228,881	150,000		138,999
Total redeemable convertible preferred stock	104,461,636	40,743,522	$	408,000	$	396,593

The significant rights, preferences and privileges of the Company’s redeemable convertible preferred stock were as follows:

Dividends — The holders of Series A Stock, Series B Stock and Series C Stock were entitled to receive noncumulative dividends at the rate of 8% of the original issue price per share, when, as and if declared by the Board. No dividends were declared and payable for the nine months ended September 30, 2023 and 2022.

Liquidation Rights — In the event of the liquidation, dissolution, or winding up of the Company, or a deemed liquidation event, including a merger or consolidation, or a sale or other disposition of all or substantially all of the Company’s assets, the holders of shares of Series C Stock and Series B Stock were entitled to receive, before any payments were made to the holders of Series A Stock or common stock, an amount per share equal to the greater of: (i) Series C Stock and the Series B Stock original issuance price of $12.2661 and $10.2217, respectively, plus any dividends declared but unpaid; or (ii) such amount per share as would have been payable had all shares of Series C Stock and Series B Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation. Should the Company’s legally available assets be insufficient to satisfy the Series C Stock and Series B Stock liquidation preference, the funds were to be distributed with equal priority and pro rata among the holders of the Series C Stock and Series B Stock in proportion to the preferential amount each holder was otherwise entitled to receive.

After full payment to holders of the Series C Stock and Series B Stock, a payment would be made to the holders of Series A Stock, in preference to the holders of the common stock, in an amount per share equal to the greater of: (i) the Series A Stock original issuance price of $1.9720, plus any dividends declared but unpaid; or (ii) such amount per share as would have been payable had all shares of Series A Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation. Should the Company’s legally available assets be insufficient to satisfy the Series A Stock liquidation preference, the funds were to be distributed with equal priority and pro rata among the holders of the Series A Stock in proportion to the preferential amount each holder was otherwise entitled to receive.

After the payment to the holders of Series C Stock, Series B Stock and Series A Stock of the full preferential amounts, the entire remaining assets of the Company legally available for distribution were to be distributed with equal priority and pro rata among the holders of common stock in proportion to the number of shares of common stock held by them.

Conversion — Each share of Series A Stock, Series B Stock and Series C Stock was convertible at the option of a holder at any time into a number of shares of the Company’s common stock at a conversion rate, which is the Series A Stock, Series B Stock and Series C Stock original issuance price, $1.9720, $10.2217 and $12.2661, respectively, divided by the Series A Stock, Series B Stock and Series C Stock conversion price in effect at the time of conversion. If, after the issuance date of the Series A Stock, Series B Stock and Series C Stock, the Company were to issue or sell, or was deemed to have sold, additional shares of common stock at a price lower than the original issuance price of the Series A Stock or Series B Stock or Series C Stock, except for certain exceptions, the conversion price of the Series A Stock and/or the Series B Stock and Series C Stock would be adjusted. The Series A Stock, Series B Stock and Series C Stock conversion prices were initially equal to the Series A Stock, Series B Stock and Series C Stock original issue prices, and were subject to recapitalization and other adjustments, as provided in the Company’s then-current certificate of incorporation. As of December 31, 2022, the conversion rates were one-for-one.

Voting Rights — The holders of redeemable convertible preferred stock and the holders of common stock were to vote together and not as separate classes. Each holder of Series A Stock, Series B Stock and Series C Stock was entitled to the number of votes equal to the number of shares of common stock into which the shares of Series A Stock, Series B Stock and Series C Stock could be converted as of the record date.

For as long shares of redeemable convertible preferred stock remained outstanding, Series A stockholders, Series B stockholders and Series C stockholders, voting as a separate class, were entitled to elect Series A, Series B and Series C members of the Board and had certain protective provisions, as defined in the then-current certificate of incorporation. The holders of redeemable convertible preferred stock and Class A Common Stock, voting together as a single class on an as-converted basis, were entitled to elect three mutual directors.

Redemption — The redeemable convertible preferred stock is recorded in mezzanine equity because while it is not mandatorily redeemable, it will become redeemable at the option of the preferred stockholders upon the occurrence of certain deemed liquidation events that are considered not solely within the Company’s control.

Equity Incentive Plan - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Number of Options
Outstanding, beginning balance (in shares) \| shares	5,036,946
Options granted (in shares) \| shares	4,771,615
Options exercised (in shares) \| shares	(40,570)
Options forfeited (in shares) \| shares	(1,063,529)
Outstanding, ending balance (in shares) \| shares	8,704,462	5,036,946
Exercisable (in shares) \| shares	1,347,153
Vested and expected to vest (in shares) \| shares	8,704,462
Weighted-Average Exercise Price Per Share
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 4.7872
Options granted (in dollars per share) \| $ / shares	16.8645
Options exercised (in dollars per share) \| $ / shares	0.7700
Options forfeited (in dollars per share) \| $ / shares	10.9236
Outstanding, ending balance (in dollars per share) \| $ / shares	10.6860	$ 4.7872
Exercisable (in dollars per share) \| $ / shares	4.3478
Vested and expected to vest (in dollars per share) \| $ / shares	$ 10.6860
Weighted-Average Remaining Contractual Term
Outstanding	8 years 10 months 24 days	9 years 6 months
Exercisable	6 years 8 months 12 days
Vested and expected to vest	8 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding \| $	$ 26,543	$ 5,488
Exercisable \| $	8,028
Vested and expected to vest \| $	$ 26,543

Common Stock

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Common Stock

On May 9, 2023, immediately prior to the IPO closing, each share of the Company’s Class A Common Stock then issued and outstanding was reclassified and became one share of the Company’s common stock. As of September 30, 2023 and December 31, 2022, there were no shares of Class B Common Stock outstanding.

As of September 30, 2023 and December 31, 2022, the Company’s common stock reserved for future issuance was as follows:


	September 30,	December 31,
	2023	2022
Shares available for future grants under Equity Incentive Plan	4,700,672	1,570,353
Outstanding stock options	8,704,462	5,036,946
Performance-based restricted stock units	2,988,492	-
Outstanding restricted stock units	2,183,413	1,107,213
Options assumed upon ValenzaBio acquisition	1,249,811	—
ESPP Shares available for future grants	900,000	—
Redeemable convertible preferred stock	—	40,743,522
Total shares reserved for future issuance	20,726,850	48,458,034

Founders’ Common Stock

On the IPO closing date, according to the terms of the restated certificate of incorporation, each share of the founders’ Class A Common Stock issued and outstanding was reclassified and became 1 share of the Company’s common stock; no vesting or other terms were modified.

In July 2020, the Company issued 2,839,749 shares of its common stock to founders at a price of $0.00002 per share. The issuance price was the estimated fair value of the shares as the shares were issued at inception and no intellectual property was contributed by the founders. The founders have voting rights and rights to receive dividends regardless of the vesting of the shares. Issued shares vest monthly over 48 months, as founders continue providing services to the Company. The Company has the right to repurchase unvested shares at the price paid by the founders if services are terminated. Stock-based compensation expense was minimal for these shares. In December 2022, the Company repurchased 591,613 restricted common shares at the original purchase price that were unvested as of the date of repurchase in connection with one founder’s resignation. As of September 30, 2023 and December 31, 2022, 295,803 and 562,032 shares were unvested, respectively. During the three and nine months ended September 30, 2023, 88,743 and 266,229 founders’ shares vested, respectively.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Redeemable Convertible Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2023

Temporary Equity [Abstract]

Schedule of Convertible Preferred Stock


	Shares Authorized	Shares Issued and Outstanding	Aggregate Liquidation Preference		Net Carrying Value
Series A redeemable convertible preferred stock	8,000,000	4,056,795	$	8,000	$	7,916
Series B redeemable convertible preferred stock	48,230,900	24,457,846	250,000		249,678
Series C redeemable convertible preferred stock	48,230,736	12,228,881	150,000		138,999
Total redeemable convertible preferred stock	104,461,636	40,743,522	$	408,000	$	396,593

Insider Trading Arrangements

3 Months Ended

9 Months Ended

Sep. 30, 2023

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

During the three months ended September 30, 2023, the directors and officers (as defined in Rule 16a-1(f) under the Exchange Act) of the Company adopted or terminated the contracts, instructions or written plans for the purchase or sale of the Company’s securities set forth in the table below.

Type of Trading Arrangement

Name and Position

Action

Date

Rule 10b5-1*

Non-rule 10b5-1**

Total Shares of Common Stock to be Sold

Expiration Date

Shao-Lee Lin, M.D., Ph.D.,

Founder & Chief Executive Officer

Adoption

August 14, 2023

Up to 315,995(1)

March 1, 2025

Melanie Gloria,

Chief Operating Officer

Adoption

August 14, 2023

Up to 80,000

November 30, 2024

Mina Kim,

Chief Legal and Administrative Officer

Adoption

August 14, 2023

Up to 100,000

December 30, 2024

Ron Oyston,

Chief People Officer

Adoption

August 14, 2023

Up to 15,200

November 1, 2024

Paul M. Peloso, M.D.,

Chief Medical Officer

Adoption

August 14, 2023

Up to 42,202

November 30, 2024

* Contract, instruction or written plan intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) under the Exchange Act.

** “Non-Rule 10b5-1 trading arrangement” as defined in Item 408(c) of Regulation S-K under the Exchange Act.

(1)Includes: (i) 100,000 shares of common stock; and (ii) up to 215,995 shares of common stock subject to restricted stock unit awards that may vest and be released to Dr. Lin on or prior to March 1, 2025 upon satisfaction of the applicable service conditions. The actual number of shares subject to restricted stock unit awards that will be released to Dr. Lin and sold under the Rule 10b5-1 trading arrangement will be net of the number of shares withheld to satisfy tax withholding obligations arising from the vesting of such awards and is not yet determinable.

Non-Rule 10b5-1 Arrangement Adopted

false

Rule 10b5-1 Arrangement Terminated

false

Non-Rule 10b5-1 Arrangement Terminated

false

Shao-Lee Lin, M.D., Ph.D. [Member]

Trading Arrangements, by Individual

Arrangement Duration

565 days

Melanie Gloria [Member]

Trading Arrangements, by Individual

Arrangement Duration

474 days

Mina Kim [Member]

Trading Arrangements, by Individual

Arrangement Duration

504 days

Ron Oyston [Member]

Trading Arrangements, by Individual

Arrangement Duration

445 days

Paul M. Peloso, M.D. [Member]

Trading Arrangements, by Individual

Arrangement Duration

474 days

Directors And Officers Trading Arrangement [Member]

Trading Arrangements, by Individual

Rule 10b5-1 Arrangement Adopted

true

Directors And Officers Trading Arrangement [Member] | Shao-Lee Lin, M.D., Ph.D. [Member]

Trading Arrangements, by Individual

Name

Shao-Lee Lin, M.D., Ph.D.

Title

Founder & Chief Executive Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

August 14, 2023

Aggregate Available

315,995

Directors And Officers Trading Arrangement [Member] | Melanie Gloria [Member]

Trading Arrangements, by Individual

Name

Melanie Gloria

Title

Chief Operating Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

August 14, 2023

Aggregate Available

80,000

Directors And Officers Trading Arrangement [Member] | Mina Kim [Member]

Trading Arrangements, by Individual

Name

Mina Kim

Title

Chief Legal and Administrative Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

August 14, 2023

Aggregate Available

100,000

Directors And Officers Trading Arrangement [Member] | Ron Oyston [Member]

Trading Arrangements, by Individual

Name

Ron Oyston

Title

Chief People Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

August 14, 2023

Aggregate Available

15,200

Directors And Officers Trading Arrangement [Member] | Paul M. Peloso, M.D. [Member]

Trading Arrangements, by Individual

Name

Paul M. Peloso, M.D.

Title

Chief Medical Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

August 14, 2023

Aggregate Available

42,202

Directors And Officers Trading Arrangement, Common Stock [Member] | Shao-Lee Lin, M.D., Ph.D. [Member]

Trading Arrangements, by Individual

Aggregate Available

100,000

Directors And Officers Trading Arrangement, Restricted Stock Unit Awards [Member] | Shao-Lee Lin, M.D., Ph.D. [Member]

Trading Arrangements, by Individual

Aggregate Available

215,995

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements and accompanying notes are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. The accompanying financial statements are consolidated and include the accounts of ACELRYIN, INC. and its wholly owned subsidiary, WH2, LLC (the legal successor to ValenzaBio). The subsidiary has not had any operations or any balances from its inception. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2022 included in the Final Prospectus filed with the SEC on May 5, 2023. The information as of December 31, 2022, included in the condensed consolidated balance sheets was derived from the Company’s audited consolidated financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial statements. The results of operations for the nine months ended September 30, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023 or for any other interim period or for any other future year.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates estimates and assumptions, including but not limited to those related to the fair value of its derivative tranche liability, the fair value of its common stock, stock-based compensation expense, accruals for research and development expenses, valuation of deferred tax assets, and uncertain income tax positions. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Segment Information	Segment Information The Company has one operating segment. The Company’s focus is the research, development and commercialization of product candidates. The Company’s chief executive officer (“CEO”), who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.
Concentration of Credit Risk	Concentration of Credit Risk Cash and cash equivalents, and short-term marketable securities are financial instruments that potentially subject the Company to concentrations of credit risk. As of September 30, 2023, cash consists of cash deposited with one financial institution, and account balances exceed federally insured limits. The Company also has investments in money market funds, U.S. Treasury obligations, corporate debt obligations, and federal agency obligations, which can be subject to certain credit risks. The Company mitigates the risks by investing in high-grade financial instruments, limiting its exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its financial instruments.
Leases	Leases The Company adopted ASU 2016-02, “Leases (Topic 842)” accounting standard as of January 1, 2022. The contractual arrangements that meet the definition of a lease are classified as operating or finance leases and are recorded on the balance sheets as both a right-of-use asset (“ROU asset”) and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company’s incremental borrowing rate (“IBR”). Lease ROU assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The Company currently does not have any finance leases. Operating lease ROU assets are adjusted for (i) payments made at or before the commencement date, (ii) initial direct costs incurred, and (iii) tenant incentives under the lease. As the implicit rate for the operating leases are not determinable, the Company determines its IBR based on the information available at the applicable lease commencement date. The IBR is determined by using the rate of interest that the Company would pay to borrow on a collateralized basis an amount equal to the lease payments for a similar term and in a similar economic environment where the asset is located. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably certain the Company will exercise any option to extend the contract. Lease costs for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Lease liabilities are increased by interest and reduced by payments each period, and the ROU asset is amortized over the lease term. Variable lease costs are recorded when incurred. In measuring the ROU assets and lease liabilities, the Company has elected to combine lease and non-lease components. The Company excludes short-term leases, if any, having initial terms of 12 months or less at lease commencement as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term for these types of leases.
Performance-Based Restricted Stock Unit Awards	Performance-Based Restricted Stock Unit Awards Performance-based restricted stock units (“PSUs”), awarded to employees vest upon the achievement of certain performance milestones and market conditions (i.e., specified average stock price hurdle) at the end of specified performance periods, subject to continuous service through each respective vest date. The amount of expense recognized is based on the grant date fair value of the PSU tranche corresponding to the performance condition of the tranche which is considered probable. The estimated grant date fair value of the market portion of the PSUs is based on a Monte Carlo simulation under each performance condition outcome. The Monte Carlo valuation model simulates the probabilities of stock price achievement, which requires management to make a number of assumptions including a 20-trading day volume-weighted average stock price, volatility of our peers, and the risk-free interest rate. Compensation expense for each tranche of a PSU award is recognized straight-line over the period commencing on the grant date of the award and ending on the vesting date of the tranche under the PSU award. Cumulative adjustments are recorded at each reporting date to reflect subsequent changes to the estimated outcome of the performance condition until the end of the respective performance period.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies.
Fair Value Measurements	Fair Value Measurements The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 — Quoted prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s financial instruments measured at fair value on a recurring basis consist of Level 1, Level 2, and Level 3 financial instruments. Usually, marketable securities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. Corporate debt obligations, commercial paper, government agency obligations and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. The Company had no Level 3 financial assets or liabilities as of September 30, 2023. The derivative tranche liability related to the Series C financing second tranche closing (Note 10) was a Level 3 financial liability as of December 31, 2022.

- Definition

Disclosure of accounting policy for segment reporting.

+ References + Details

- Definition

Disclosure of accounting policy for award under share-based payment arrangement. Includes, but is not limited to, methodology and assumption used in measuring cost.

+ References

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+ Details

Significant Agreements	9 Months Ended
Significant Agreements	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Agreements	Significant Agreements Affibody License and Collaboration Agreement On August 9, 2021, the Company entered into a license agreement with Affibody AB (“Affibody”) (the “Affibody Agreement”) under which Affibody granted the Company exclusive, sublicensable licenses to develop, commercialize and manufacture products containing izokibep for all human therapeutic uses on a worldwide basis, subject to a pre-existing agreement with Inmagene Biopharmaceuticals (“Inmagene”) with respect to certain Asian countries. The Company chairs a global joint steering committee composed of designees from Affibody, Inmagene and the Company and retains final decision-making authority for izokibep global development. In doing so, the Company is obligated to use commercially reasonable efforts (i) to develop products containing izokibep worldwide, excluding certain defined territories, (ii) for the conduct and finalization of certain ongoing clinical trials, and (iii) to commercialize products containing izokibep for all human therapeutic uses worldwide, excluding certain defined territories, after obtaining the applicable marketing authorization. The Company is responsible for manufacturing both the clinical and commercial supply of licensed product globally. In connection with the Affibody Agreement, the Company paid a non-refundable upfront license fee in the aggregate amount of $3.0 million over the course of August 2021 and September 2021, and $22.0 million in October 2021. The Company is also obligated to pay Affibody (i) an aggregate of up to $280.0 million, $30.0 million of which would be due prior to the first approval in the United States, upon the achievement of various development, regulatory and commercialization milestones and (ii) high single-digit to low-teens royalties on net sales of licensed products in the territory where the Company has commercialization rights, subject to certain reductions. Royalties will be due on a licensed product-by-licensed product and country-by-country basis beginning after the first commercial sale of the licensed product, except in Mainland China, Hong Kong, Macau, Taiwan and South Korea, and lasting until the later of (a) the expiration of all valid patent claims or regulatory exclusivity covering the licensed product in that country and (b) ten years after such first commercial sale. In the event the U.S. Food and Drug Administration (“FDA”) grants the Company (or its affiliates or sublicensees) a priority review voucher for a licensed product, the Company will pay Affibody either: (a) if the Company sells or transfer such priority review voucher to a third-party, approximately one third of the proceeds received from the sale, net of taxes, or (b) if the Company uses the priority review voucher for an indication or product outside the scope of the Affibody Agreement, approximately one third of the fair market value of the priority review voucher as determined in accordance with the Affibody Agreement. Unless earlier terminated, the Affibody Agreement will continue on a licensed product-by-licensed product basis and country-by-country basis until there are no more royalty payments owed to Affibody on any licensed product thereunder. The acquisition of the exclusive license was accounted for as an in-process research and development asset acquisition and as the acquired technology did not have an alternative use, the total consideration of $25.0 million was recorded as research and development expense in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2021. Milestone payments are contingent consideration and are accrued when contingent events occur and achievement of milestones is probable. Royalties will be recognized as cost of sales when products are sold and royalties are payable. No milestone or royalties were probable and estimable as of September 30, 2023 and December 31, 2022. Pierre Fabre License and Commercialization Agreement Upon the closing of the Acquisition, the Company became the successor to ValenzaBio’s rights under the March 25, 2021 license and commercialization agreement between ValenzaBio and Pierre Fabre, as amended (the “Pierre Fabre Agreement”). The Company received certain exclusive worldwide licenses, with the right to sublicense, to certain patents, know-how and other intellectual property to develop, manufacture, use and commercialize lonigutamab for non-oncology therapeutic indications. The license from Pierre Fabre extends to any product containing lonigutamab (excluding any fragments or derivatives) as its sole active ingredient (each, a “PF Licensed Product”). The Pierre Fabre Agreement prohibits the Company from using the licensed intellectual property in any antibody drug conjugate, multi-specific antibodies or any other derivatives of lonigutamab. In the event the Company decides to sublicense the rights to develop or commercialize a PF Licensed Product in any territory outside of the United States and Canada, Pierre Fabre retains the right of first negotiation to acquire such development and commercialization rights in one or more countries in such territory. Subject to the validation of certain clinical trial criteria by a joint steering committee, Pierre Fabre has the option to reclaim all exclusive rights to develop, commercialize and exploit the PF Licensed Product in such territories and to obtain an exclusive sublicensable license in such territories for any improvements and trademarks to such PF Licensed Product, and to exploit such PF Licensed Product for non-oncology therapeutic indications, subject to certain payment obligations. If Pierre Fabre exercises such option, and intends to sublicense such rights, then the Company has the right of first negotiation to acquire such development and commercialization rights as to that territory, or Pierre Fabre has the right to require the Company to buy out its right to the option for a one-time payment of $31.0 million or the Company has the right to choose to buy out Pierre Fabre’s option by making the one-time payment of $31.0 million within 30 days from Pierre Fabre’s notice of exercise of such option. If Pierre Fabre does not exercise its option within the option period or if the Company buys out Pierre Fabre’s right to the option, the option will expire or terminate, respectively. The Company is solely responsible for the development, regulatory approvals and commercialization of each PF Licensed Product except to the extent that Pierre Fabre reclaims rights to a PF Licensed Product in the option territory. As consideration for the amendment to the Pierre Fabre Agreement, which became effective upon the closing of the Acquisition (see Note 3), the Company paid Pierre Fabre an aggregate license payment of $10.0 million. The Company is also obligated to (i) make payments of up to $99.5 million upon the achievement of various development and regulatory milestones, (ii) make milestone payments of up to $390.0 million upon the achievement of certain commercial milestones, and (iii) pay tiered royalties in the high single-digit to low-teen percentages to Pierre Fabre on worldwide net sales in a given calendar year. Royalties will be payable for each PF Licensed Product in a given country during a period commencing upon the first commercial sale of such PF Licensed Product in such country and continuing until the latest of (a) 10 years after such first commercial sale, (b) expiration of last-to-expire valid claim in a licensed patent in such country and (c) expiration of regulatory exclusivity for such PF Licensed Product in such country. In the event the Company enters into a sublicense with a third party, the Company must also share with Pierre Fabre a percentage of any revenues from option fees, upfront payments, license maintenance fees, milestone payments or the like generated from the sublicense. Such percentage may be between the high single-digits to the low thirties based on which stage of development of a PF Licensed Product the sublicense relates to. Unless earlier terminated, the Pierre Fabre Agreement will continue on a PF Licensed Product-by-PF Licensed Product and country-by-country basis until there are no more royalty payments owed to Pierre Fabre on any PF Licensed Product thereunder. Either party may terminate the Pierre Fabre Agreement upon an uncured material breach, or upon the bankruptcy or insolvency of the other party. Pierre Fabre may also terminate the agreement if the Company or any of its affiliates institutes a patent challenge against the licensed patents from Pierre Fabre. The Company may also terminate the Pierre Fabre Agreement with or without cause upon nine months’ prior written notice, so long as there is no ongoing clinical trial for any PF Licensed Product. As of September 30, 2023, no milestones were probable and accrued in the condensed consolidated balance sheet. The payment of $10.0 million for additional license fees was recorded as research and development expenses in the condensed consolidated statement of operations and comprehensive loss for the nine months ended September 30, 2023. Novelty Nobility License and Commercialization Agreement Upon the closing of the Acquisition, the Company became the successor to an exclusive license agreement between ValenzaBio and Novelty Nobility (the “Novelty License Agreement”) and obtained a worldwide exclusive license for the development and commercialization of SLRN-517, an unmodified IgG1 monoclonal antibody, as a therapeutic treatment. In connection with the arrangement, the Company is obligated to (i) make development and regulatory milestones of up to $44.3 million, (ii) make commercial sales milestone payments of up to $682.0 million and (iii) pay tiered royalties of a low single-digit to high-single-digit percentage on future worldwide net sales. The Novelty License Agreement is effective on a licensed product-by-licensed product and country-by-country basis until the expiration of the latest to expire royalty term, unless early terminated. The royalty term, with respect to a licensed product and a country is the period commencing on the first commercial sale of such product in such country, and ending upon the latest to occur of: a) there being no patent right in such country that had at least one valid claim covering the licensed product in whole or in part, or the manufacture or use thereof; b) 10 years from the first commercial sale of such product worldwide; or c) expiration of regulatory exclusivity for such product in such country. The agreement can be early terminated upon (i) a material breach, (ii) abandonment of development by the Company, in which the Company ceases all development activities for the licensed product, (iii) termination by patent challenge, and (iv) insolvency. The Company may terminate the contract at any point, upon 30 days prior written notice to Novelty Nobility, Inc. As of September 30, 2023, no milestones were probable and accrued in the condensed consolidated balance sheet.

Condensed Consolidated Statements of Cash Flows (Parenthetical)	3 Months Ended
	Jun. 30, 2023 shares
Common Stock
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)	40,743,522

Consolidated Balance Sheet Components - Schedule of Accrued Compensation and Other Current Liabilities (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation	$ 4,016,000	$ 3,068,000
Accrued professional service fees	751,000	808,000
Other accrued expenses and current liabilities	377,000	361,000
Total	5,144,000	4,237,000
Offering costs	$ 0	$ 200,000

Fair Value Measurements - Summary of Changes in Level 3 Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of December 31, 2022	$ 10,291
Change in fair value	(10,291)
Balance as of September 30, 2023	$ 0

ValenzaBio Acquisition - Schedule of Allocation of Purchase Consideration (Details) - ValenzaBio Asset Acquisition $ in Thousands	Jan. 04, 2023 USD ($)
Asset Acquisition [Line Items]
Cash	$ 11,369
Prepaid expenses and other current assets	2,074
In-process research and development assets	123,057
Accounts payable	(1,628)
Accrued research and development expenses	(4,805)
Accrued compensation and other current liabilities	(53)
Total net asset acquired	$ 130,014

Consolidated Balance Sheet Components - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid insurance and other current assets	$ 1,834	$ 86
Prepaid research and development expenses	1,645	682
VAT receivable	1,292	0
Prepaid other services	776	288
Interest receivable	660	138
Research and development credit receivable	0	250
Total	$ 6,207	$ 1,444

Consolidated Balance Sheet Components - Schedule of Prepaid and Other Noncurrent Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid research and development expenses, non-current	$ 2,448	$ 1,964
Security deposits	34	0
Deferred IPO offering costs	0	774
Acquisition transaction costs	0	1,121
Total	$ 2,482	$ 3,859

Condensed Consolidated Balance Sheets - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 381,738,000	$ 267,110,000
Short-term marketable securities	406,693,000	47,510,000
Prepaid expenses and other current assets	6,207,000	1,444,000
Total current assets	794,638,000	316,064,000
Prepaid expenses and other assets, non-current	2,482,000	3,859,000
Operating lease, right-of-use asset	1,240,000	0
Property, plant and equipment, net	2,129,000	0
Total assets	800,489,000	319,923,000
Current liabilities
Accounts payable	18,702,000	5,947,000
Accrued research and development expenses	41,295,000	5,717,000
Accrued compensation and other current liabilities	5,144,000	4,237,000
Severance liability	1,720,000	0
Total current liabilities	66,861,000	15,901,000
Derivative tranche liability	0	10,291,000
Operating lease liability, non-current	1,252,000	0
Total liabilities	68,113,000	26,192,000
Commitments and contingencies (Note 8)
Redeemable convertible preferred shares, no par value; no shares authorized, issued and outstanding as of September 30, 2023; 104,461,636 shares authorized as of December 31, 2022; par value of $0.00001 per share; 40,743,522 shares issued and outstanding as of December 31, 2022; aggregate liquidation preference $408,000 as of December 31, 2022	0	396,593,000
Stockholders’ equity (deficit)
Preferred stock, 10,000,000 shares authorized, $0.00001 par value, no shares issued and outstanding at September 30, 2023; no shares authorized, issued, and outstanding at December 31, 2022	0	0
Common stock, par value of $0.00001 per share; 790,000,000 and 229,461,636 shares authorized as of September 30, 2023 and December 31, 2022, respectively; 97,240,419 and 2,767,359 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	1,000	0
Additional paid-in capital	1,125,932,000	4,302,000
Accumulated other comprehensive loss	(50,000)	(86,000)
Accumulated deficit	(393,507,000)	(107,078,000)
Total stockholders' equity (deficit)	732,376,000	(102,862,000)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	$ 800,489,000	$ 319,923,000

Fair Value Measurements - Schedule of Cash and Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 781,555	$ 285,733
Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	374,862	238,223
Short-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 406,693	$ 47,510

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party TransactionsDuring the nine months ended September 30, 2022, the Company reimbursed one of its investors $10,000 for Series B Stock issuance costs.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Equity Incentive Plan - Schedule of Valuation Assumptions (Details) - Stock options	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility minimum	87.34%		75.30%	99.99%
Expected volatility maximum	87.93%		92.20%	102.81%
Expected volatility		99.91%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)		6 years 29 days
Risk-free interest rate minimum	4.14%		3.30%	1.69%
Risk-free interest rate maximum	4.61%		4.61%	3.26%
Risk-free interest rate		3.05%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	5 years 11 months 12 days		5 years 9 months 7 days	5 years 10 months 24 days
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	6 years 14 days		6 years 29 days	6 years 29 days

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)
Beginning balance (in shares) at Dec. 31, 2021	16,285,718
Beginning balance at Dec. 31, 2021	$ 132,620
Redeemable Convertible Preferred Stock
Issuance of redeemable convertible preferred stock (in shares)	12,228,923
Issuance of redeemable convertible preferred stock	$ 124,974
Ending balance (in shares) at Mar. 31, 2022	28,514,641
Ending balance at Mar. 31, 2022	$ 257,594
Beginning balance (in shares) at Dec. 31, 2021		2,860,032
Beginning balance at Dec. 31, 2021	(42,056)	$ 0	$ 250	$ (42,306)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock awards (in shares)		498,940
Stock-based compensation expense	1,610		1,610
Net loss	(16,085)			(16,085)
Ending balance (in shares) at Mar. 31, 2022		3,358,972
Ending balance at Mar. 31, 2022	$ (56,531)	$ 0	1,860	(58,391)	0
Beginning balance (in shares) at Dec. 31, 2021	16,285,718
Beginning balance at Dec. 31, 2021	$ 132,620
Ending balance (in shares) at Sep. 30, 2022	40,743,522
Ending balance at Sep. 30, 2022	$ 396,592
Beginning balance (in shares) at Dec. 31, 2021		2,860,032
Beginning balance at Dec. 31, 2021	(42,056)	$ 0	250	(42,306)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(44,965)
Unrealized gain on short-term marketable securities, net	(200)
Ending balance (in shares) at Sep. 30, 2022		3,358,972
Ending balance at Sep. 30, 2022	$ (84,682)	$ 0	2,789	(87,271)	(200)
Beginning balance (in shares) at Mar. 31, 2022	28,514,641
Beginning balance at Mar. 31, 2022	$ 257,594
Ending balance (in shares) at Jun. 30, 2022	28,514,641
Ending balance at Jun. 30, 2022	$ 257,594
Beginning balance (in shares) at Mar. 31, 2022		3,358,972
Beginning balance at Mar. 31, 2022	(56,531)	$ 0	1,860	(58,391)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	369		369
Net loss	(14,474)			(14,474)
Unrealized gain on short-term marketable securities, net	(138)				(138)
Ending balance (in shares) at Jun. 30, 2022		3,358,972
Ending balance at Jun. 30, 2022	$ (70,774)	$ 0	2,229	(72,865)	(138)
Redeemable Convertible Preferred Stock
Issuance of redeemable convertible preferred stock (in shares)	12,228,881
Issuance of redeemable convertible preferred stock	$ 138,998
Ending balance (in shares) at Sep. 30, 2022	40,743,522
Ending balance at Sep. 30, 2022	$ 396,592
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	560		560
Net loss	(14,406)			(14,406)
Unrealized gain on short-term marketable securities, net	(62)				(62)
Ending balance (in shares) at Sep. 30, 2022		3,358,972
Ending balance at Sep. 30, 2022	$ (84,682)	$ 0	2,789	(87,271)	(200)
Beginning balance (in shares) at Dec. 31, 2022	40,743,522
Beginning balance at Dec. 31, 2022	$ 396,593
Ending balance (in shares) at Mar. 31, 2023	40,743,522
Ending balance at Mar. 31, 2023	$ 396,593
Beginning balance (in shares) at Dec. 31, 2022	2,767,359	2,767,359
Beginning balance at Dec. 31, 2022	$ (102,862)	$ 0	4,302	(107,078)	(86)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with ValenzaBio acquisition (in shares)		18,885,731
Issuance of common stock in connection with ValenzaBio acquisition	128,735		128,735
Stock-based compensation expense	7,139		7,139
Net loss	(176,450)			(176,450)
Unrealized gain on short-term marketable securities, net	86				86
Ending balance (in shares) at Mar. 31, 2023		21,653,090
Ending balance at Mar. 31, 2023	$ (143,352)	$ 0	140,176	(283,528)	0
Beginning balance (in shares) at Dec. 31, 2022	40,743,522
Beginning balance at Dec. 31, 2022	$ 396,593
Ending balance (in shares) at Sep. 30, 2023	0
Ending balance at Sep. 30, 2023	$ 0
Beginning balance (in shares) at Dec. 31, 2022	2,767,359	2,767,359
Beginning balance at Dec. 31, 2022	$ (102,862)	$ 0	4,302	(107,078)	(86)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)	40,570
Net loss	$ (286,429)
Unrealized gain on short-term marketable securities, net	$ 36
Ending balance (in shares) at Sep. 30, 2023	2,767,359	97,240,419
Ending balance at Sep. 30, 2023	$ 732,376	$ 1	1,125,932	(393,507)	(50)
Beginning balance (in shares) at Mar. 31, 2023	40,743,522
Beginning balance at Mar. 31, 2023	$ 396,593
Redeemable Convertible Preferred Stock
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)	(40,743,522)
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering	$ (396,593)
Ending balance (in shares) at Jun. 30, 2023	0
Ending balance at Jun. 30, 2023	$ 0
Beginning balance (in shares) at Mar. 31, 2023		21,653,090
Beginning balance at Mar. 31, 2023	(143,352)	$ 0	140,176	(283,528)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon initial public offering, net of underwriting discounts commissions and issuance costs of $47,354 (in shares)		34,500,000
Issuance of common stock upon initial public offering, net of underwriting discounts commissions and issuance costs of $47,354	573,644		573,644
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)		40,743,522
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering	396,593	$ 1	396,592
Issuance of common stock upon settlement of restricted stock units, net of shares withheld for taxes (in shares)		303,237
Issuance of common stock upon settlement of restricted stock units, net of shares withheld for taxes	(8,325)		(8,325)
Stock-based compensation expense	8,501		8,501
Net loss	(26,039)			(26,039)
Unrealized gain on short-term marketable securities, net	44				44
Ending balance (in shares) at Jun. 30, 2023		97,199,849
Ending balance at Jun. 30, 2023	$ 801,066	$ 1	1,110,588	(309,567)	44
Ending balance (in shares) at Sep. 30, 2023	0
Ending balance at Sep. 30, 2023	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	15,313		15,313
Issuance of common stock upon exercise of options (in shares)		40,570
Issuance of common stock upon exercise of options	31		31
Net loss	(83,940)			(83,940)
Unrealized gain on short-term marketable securities, net	$ (94)				(94)
Ending balance (in shares) at Sep. 30, 2023	2,767,359	97,240,419
Ending balance at Sep. 30, 2023	$ 732,376	$ 1	$ 1,125,932	$ (393,507)	$ (50)

Equity Incentive Plan

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Equity Incentive Plan

Equity Incentive Plans

In April 2023, the Company’s board of directors adopted, and stockholders approved, the 2023 Equity Incentive Plan (the “2023 Plan”) that became effective on May 4, 2023. The Company reserved 12,000,000 new shares of common stock for issuance under the 2023 Plan. In addition, 6,920,846 shares issued and outstanding under the Company’s 2020 Equity Incentive Plan, as amended (the “2020 Plan”), may be added to the 2023 Plan as such shares become available from time to time if awards terminate, expire, or lapse for any reason without the delivery of shares, or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. The 2023 Plan also provides that the number of shares initially reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2024 and ending on January 1, 2033, by an amount equal to the lesser of (i) 5% of the shares of common stock outstanding on the last day of the immediately preceding fiscal year, and (ii) such smaller number of shares of stock as determined by the Company’s board of directors. No more than 56,762,538 shares of stock may be issued upon the exercise of incentive stock options under the 2023 Plan. The Company may grant incentive stock options, nonstatutory stock options (“NSOs”), restricted stock units (“RSUs”), restricted stock awards (“RSAs”), stock appreciation rights (“SARs”), performance awards and other awards to the Company’s officers, employees, directors and consultants. Options under the 2023 Plan may be granted for periods of up to 10 years at exercise prices no less than the fair market value of the common stock on the date of grant and usually vest over four years. The exercise price of an option granted to a 10% stockholder may not be less than 110% of the fair market value of the shares on the date of grant and such option may not be exercisable after the expiration of five years from the date of grant. The grant date fair market value of all awards made under our 2023 Plan and all cash compensation paid by us to any non-employee director for services as a director in any fiscal year may not exceed $750,000, increased to $1,000,000 in the fiscal year of their initial service as a non-employee director. The 2023 Plan is the successor to and continuation of the 2020 Plan and no additional awards may be granted under the 2020 Plan. All outstanding awards granted under the 2020 Plan will remain subject to the terms of the 2020 Plan. The 2020 Plan provided for the grant of incentive stock options, nonstatutory stock options, RSUs and RSAs to the Company’s officers, employees, directors and consultants. As of September 30, 2023, 4,661,603 shares of the Company’s common stock were reserved for issuance under the 2023 Plan.

In April 2023, the Company’s board of directors and stockholders adopted the 2023 Employee Stock Purchase Plan (the “ESPP”), which became effective on May 4, 2023. The ESPP authorized issuance of up to 900,000 shares of common stock. The ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. Employees purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value at the start or end of six-month purchase and offering consecutive periods. The aggregate number of shares reserved for sale under the 2023 ESPP will increase automatically on January 1 for a period of up to 10 calendar years, commencing on January 1, 2024, by the number of shares equal to the lesser of 1% of the Company's total outstanding shares of common stock on the immediately preceding December 31st, and 2,700,000 shares or a lesser number of shares as may be determined by the board of directors.

Stock Options

Stock options issued under the 2020 Plan and 2023 Plan generally vest over a four-year period and expire ten years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the individual award agreements and the Company’s severance policies.

A summary of option activity under the 2020 Plan and 2023 Plan is as follows:


	Number of Options	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022	5,036,946	$	4.7872	9.5	$	5,488
Options granted	4,771,615	$	16.8645
Options exercised	(40,570)	0.7700
Options forfeited	(1,063,529)	10.9236
Outstanding at September 30, 2023	8,704,462	$	10.6860	8.9	$	26,543
Exercisable at September 30, 2023	1,347,153	$	4.3478	6.7	$	8,028
Vested and expected to vest at September 30, 2023	8,704,462	$	10.6860	8.9	$	26,543

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock at September 30, 2023 and December 31, 2022. Fair value of shares vested during the three and nine months ended September 30, 2023 was $6.0 million and $7.8 million, respectively. The weighted-average grant date fair value of options granted during the three and nine months ended September 30, 2023 was $16.90 and $13.69, respectively.

ValenzaBio 2020 Stock Option Plan

On January 4, 2023, in connection with the Acquisition, the Company assumed the ValenzaBio 2020 Stock Option Plan and options to issue 1,249,811 shares of the Company’s Class A Common Stock to ValenzaBio option holders, who entered into consulting agreements with the Company. The weighted-average exercise price of assumed options was $3.6736 per share.

Under the terms of the Merger Agreement, the assumed options vested in full on March 31, 2023. No options were exercised for the three and nine months ended September 30, 2023.

The Company recognized the full amount of stock-based compensation expense of $4.9 million, including $3.1 million as research and development expenses and $1.8 million as general administrative expenses, related to assumed options in the condensed consolidated statement of operations for the nine months ended September 30, 2023.

Restricted Stock Units

In 2022, the Company granted RSU awards for 1,107,213 shares vesting based on satisfaction of certain service and liquidity conditions. On March 23, 2023, the Board approved the acceleration of vesting of 138,401 RSUs. The Company accounted for the changes in vesting terms as a modification and re-measured modified awards at fair value on the modification date.

The estimated fair value of RSUs granted was $8.0 million after modification.

On May 9, 2023, the IPO closing date, 640,416 RSUs vested and the Company recognized $5.5 million stock-based compensation expense. The Company issued 303,237 shares and withheld 337,179 shares to satisfy tax withholding obligations of $8.3 million paid upon the RSU settlement. 466,797 RSUs remained unvested as of September 30, 2023.

On August 16, 2023, the Company granted RSU awards for 1,725,168 shares to certain employees of the Company, which shall vest in four equal installments beginning on May 15, 2024, subject to the employee’s continuous service through each applicable vesting date.

Performance-Based Restricted Stock Units

In August 2023, the Company granted PSUs to certain employees and officers of the Company. The PSUs may vest over several years subject to the achievement of (i) certain clinical development milestones over a performance period from the grant date to May 2027 (the “Performance Period”) or (ii) market conditions (i.e., stock price hurdle) based on pre-specified volume-weighted average stock price measurements as of each vesting performance measurement date, and continued employment with the Company through the applicable vesting date(s). The target number of shares under the PSUs is 3,135,104. The ultimate number of PSU shares that may vest, in the aggregate over the Performance Period, could in certain cases be up to 150% of the target number of shares upon the achievement of certain market or performance conditions.

A summary of PSU activity based on the target number of shares is presented in the following table:


	Number of PSUs	Weighted-Average Grant Date Fair Value*
Outstanding at December 31, 2022	—	$	—
Granted	3,135,104	$	27.43
Vested	—	$	—
Forfeited	(146,612)	$	27.43
Outstanding at September 30, 2023	2,988,492	$	27.43

*The grant date fair value is based only on the PSUs with market conditions and does not factor in any performance conditions.

As the PSUs granted in 2023 are subject to a market condition, the grant date fair value for such PSUs was based on a Monte Carlo simulation model. The Company estimated the fair value of PSUs based on the grant date price of its common stock of $26.97 and the following assumptions: expected volatility of 87.71%, risk-free-rate of 4.47%, and zero expected dividend yield. In 2023, the Company granted PSUs to employees with a weighted-average grant date fair value of $27.43. The unvested awards will expire if it is determined that the vesting conditions have not been met during the applicable three-year performance period.

2023 Employee Stock Purchase Plan

The first purchase period commenced on June 15, 2023 and will end on December 14, 2023. The Company recorded $0.3 million in accrued liabilities as of September 30, 2023.

Stock-Based Compensation Expense


	Three Months Ended September 30,	Three Months Ended September 30,	Nine Months Ended September 30,	Nine Months Ended September 30,
	2023	2022	2023	2022

Expected volatility	87.34% - 87.93%	99.91%	75.30% - 92.20%	99.99% - 102.81%
Expected dividend yield	0%	0%	0%	0%
Expected term (in years)	5.95 – 6.04 years	6.08 years	5.77 - 6.08 years	5.90 - 6.08 years
Risk-free interest rate	4.14% - 4.61%	3.05%	3.30% - 4.61%	1.69% - 3.26%

The following table presents the classification of stock-based compensation expense related to awards granted under its equity incentive plans (in thousands):


	Three Months ended September 30,				Nine Months ended September 30,
	2023		2022		2023		2022
General and administrative expenses	$	11,741	$	196	$	22,292	$	1,677
Research and development expenses	3,572		364		8,661		862
Total stock-based compensation expense	$	15,313	$	560	$	30,953	$	2,539

The stock-based compensation expense relates to the following equity-based awards:


	Three Months ended September 30,				Nine Months ended September 30,
	2023		2022		2023		2022
Restricted stock units	$	2,345	$	—	$	7,884	$	—
Performance-based restricted stock units	4,265		—		4,265		—
Stock options	8,577		560		18,661		1,234
ESPP	126		—		143		—
Restricted stock awards	—		—		—		1,305
Total stock-based compensation expense	$	15,313	$	560	$	30,953	$	2,539

The Company recognized $4.9 million stock-based compensation expense related to assumed ValenzaBio options and $0.9 million related to unvested options and RSAs net-settled at the closing of the Acquisition. As of September 30, 2023, there was $63.2 million of unrecognized stock-based compensation expense related to granted stock options, which is expected to be recognized over a weighted-average period of 3.4 years. As of September 30, 2023, there was $46.4 million of unrecognized stock-based compensation expense related to RSUs which will be recognized over the remaining vesting term through May 2027. The Company recognized $4.3 million in compensation expense during the three and nine months ended September 30, 2023 related to PSUs. This expense is related only to the market conditions. As of September 30, 2023, the Company evaluated the clinical development milestone performance conditions and determined them to be not probable of achievement. As of September 30, 2023, total compensation cost not yet recognized related to unvested PSUs was $77.7 million, which is expected to be recognized over a weighted-average period of 2.5 years. Total compensation cost not recognized related to unvested PSUs can increase up to $104.6 million depending on the future achievement of PSUs performance conditions.

Equity Incentive Plan - Summary of Performance Share Activity (Details) - Performance-based restricted stock units	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Number of PSUs
Outstanding at beginning of period (in shares) \| shares	0
Granted (in shares) \| shares	3,135,104
Vested (in shares) \| shares	0
Forfeited (in shares) \| shares	(146,612)
Outstanding at end of period (in shares) \| shares	2,988,492
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) \| $ / shares	$ 0
Granted (in dollars per share) \| $ / shares	27.43
Vested (in dollars per share) \| $ / shares	0
Forfeited (in dollars per share) \| $ / shares	27.43
Outstanding at end of period (in dollars per share) \| $ / shares	$ 27.43

Consolidated Balance Sheet Components - Property, Plant and Equipment (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 2,196,000
Less: accumulated depreciation and amortization	(67,000)
Property, plant and equipment, net	2,129,000	$ 0
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,499,000
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	263,000
Computer and other equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	344,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 90,000

Net Loss Per Share Attributable to Common Stockholders

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Numerator:
Net loss	$	(83,940)	$	(14,406)	$	(286,429)	$	(44,965)
Denominator:
Weighted average common shares outstanding	97,227,070		3,358,972		61,580,296		3,268,666
Less: Weighted-average common shares subject to repurchase	(354,323)		(1,594,679)		(442,191)		(1,848,467)
Weighted-average common shares outstanding, basic and diluted	96,872,747		1,764,293		61,138,105		1,420,199
Net loss per share attributable to common stockholders, basic and diluted	$	(0.87)	$	(8.17)	$	(4.68)	$	(31.66)

The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive:


	As of September 30,
	2023	2022
Outstanding options to purchase common stock	8,704,462	2,598,180
Unvested RSUs outstanding	2,183,413	451,247
Outstanding options to purchase common stock assumed upon the ValenzaBio acquisition	1,249,811	0
Common stock subject to repurchase	295,803	1,477,641
Redeemable convertible preferred stock	0	40,743,522
Total	12,433,489	45,270,590

The table above does not include contingently issuable PSUs with performance vesting conditions, which as of September 30, 2023 were not deemed probable to be achieved (see Note 12).

Available-For-Sale Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-Sale Marketable Securities

The following tables summarize the estimated fair value of the Company’s available-for-sale marketable securities as of September 30, 2023 and December 31, 2022 (in thousands):


As of September 30, 2023:	Total Amortized Cost		Total Unrealized Gains		Total Unrealized Loss		Total Estimated Fair Value

Money market funds (included in cash and cash equivalents)	$	84,761	$	-	$	-	$	84,761
U.S. Treasury obligations ($223,032 included in cash and cash equivalents)	514,029		51		(30)		514,050
Corporate debt obligations ($46,714 included in cash and cash equivalents)	140,923		4		(74)		140,853
Federal agency obligations ($21,347 included in cash and cash equivalents)	41,892		5		(6)		41,891
Total available for sale marketable securities	$	781,605	$	60	$	(110)	$	781,555


As of December 31, 2022:	Total Amortized Cost		Total Unrealized Loss (1)		Total Estimated Fair Value

Money market funds (included in cash and cash equivalents)	$	238,223	$	-	$	238,223
U.S. Government bonds	25,506		(47)		25,459
U.S. Treasury obligations	11,430		(26)		11,404
Corporate debt obligations	2,145		(4)		2,141
Federal agency obligations	8,515		(9)		8,506
Total available for sale marketable securities	$	285,819	$	(86)	$	285,733

(1)The Company did not have any gross unrealized gains as of December 31, 2022.

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Common Stock - Narrative (Details)	1 Months Ended		3 Months Ended	9 Months Ended
Common Stock - Narrative (Details)	Dec. 31, 2022 shares	Jul. 31, 2020 $ / shares shares	Sep. 30, 2023 shares	Sep. 30, 2023 shares	May 09, 2023
Class of Stock [Line Items]
Conversion of stock, ratio					1
Common stock, outstanding (in shares)	2,767,359		2,767,359	2,767,359
Stock issued during period, issued for services (in shares)		2,839,749
Sale of stock, price (in dollars per share) \| $ / shares		$ 0.00002
Common Class B
Class of Stock [Line Items]
Common stock, outstanding (in shares)	0		0	0
Restricted stock awards
Class of Stock [Line Items]
Vesting period		48 months
Forfeited in period (in shares)	591,613
Shares unvested (in shares)	562,032		295,803	295,803
Vested (in shares)			88,743	266,229

Derivative Tranche Liability (Details) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended			9 Months Ended
	Jun. 30, 2023 $ / shares shares	May 09, 2023 $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) $ / shares shares	Mar. 31, 2022 shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) $ / shares	Dec. 31, 2022 USD ($)	Sep. 09, 2022 USD ($)
Derivative [Line Items]
Issuance of convertible preferred stock (in shares) \| shares					12,228,881	12,228,923
Derivative tranche liability			$ 10,778		$ 10,778			$ 10,778	$ 10,291	$ 10,800
Change in fair value of derivative tranche liability				$ 0	$ 0		$ 10,291	$ 0
Probability of achieving specified conditions
Derivative [Line Items]
Derivative liability, measurement input				0.90			0.90
Discount rate
Derivative [Line Items]
Derivative liability, measurement input			0.25		0.25			0.25
Forward Contracts
Derivative [Line Items]
Derivative tranche liability			$ 10,800		$ 10,800			$ 10,800
Series C redeemable convertible preferred stock
Derivative [Line Items]
Issuance of convertible preferred stock (in shares) \| shares	12,228,881	12,228,881	12,228,881
Shares issued, price per share (in dollars per share) \| $ / shares	$ 12.2661	$ 12.2661	$ 12.2661		$ 12.2661			$ 12.2661

Derivative Tranche Liability	9 Months Ended
Derivative Tranche Liability	Sep. 30, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Tranche Liability	Derivative Tranche Liability In connection with the Series C First Tranche Closing, prior to the IPO closing, the Company had an obligation to sell, and investors of the Series C First Tranche Closing had an obligation to purchase, an additional 12,228,881 shares of Series C redeemable convertible preferred stock at $12.2661 per share on June 30, 2023. The obligation of each investor to purchase shares at the Series C Second Tranche Closing were subject to the fulfillment, on or before such closing, of certain conditions including not closing the Company’s first underwritten public offering of its Class A Common Stock under the Securities Act or the closing of a direct listing prior to June 30, 2023. The Series C Second Tranche Closing was terminated at the IPO closing, on May 9, 2023. Prior to May 9, 2023, the obligation to issue and purchase shares was concluded to be a forward contract derivative liability and was measured at fair value using a probability weighted model at the issuance date. The initial fair value of the forward contract was $10.8 million and was recorded as a derivative tranche liability. The Company used the following assumptions to estimate the liability as of the issuance date: probability of achieving milestone of 90%; expected term equals the contractual term from September 2022 until June 2023; Series C preferred stock fair value of $12.2661; and a discount rate of 25%. Following the termination of the Series C Second Tranche Closing at the closing of the IPO the Company recognized a gain on change in fair value of the derivative tranche liability in the amount of zero and $10.3 million in the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2023, respectively.

ValenzaBio Acquisition (Tables)

9 Months Ended

Sep. 30, 2023

Business Combination and Asset Acquisition [Abstract]

Asset Acquisition

The following table represents the total purchase consideration (in thousands):


Issued Class A Common Stock (1)	$	128,735
Transaction costs (2)	1,271
Cash (3)	8
Total	$	130,014

(2)Legal and advisory transaction costs of $1.3 million incurred by the Company in connection with the Acquisition, including $0.1 million payable in cash to Seller LLC for the expense fund.

(3)Cash payment of $7,663 to one non-accredited investor for settlement of vested ValenzaBio options.

The following is the allocation of the purchase consideration to the acquired assets and liabilities (in thousands):


Cash	$	11,369
Prepaid expenses and other current assets	2,074
In-process research and development assets	123,057
Accounts payable	(1,628)
Accrued research and development expenses	(4,805)
Accrued compensation and other current liabilities	(53)
Total net asset acquired	$	130,014

Fair Value Measurements - Summary of Significant Assumptions Used to Estimate Fair Value (Details)	Sep. 30, 2023	May 09, 2023	Dec. 31, 2022	Sep. 30, 2022
Probability of achieving specified conditions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input	0.90
Probability of achieving specified conditions \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input			0.80
Fair value of Series C preferred stock share \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input		12.2661	12.2661
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input				0.25
Discount rate \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input			0.25

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Schedule of Financial Instruments Measured on Recurring Basis

The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands):


	Fair Value Measurements as of September 30, 2023
As of September 30, 2023:	Total		Level 1		Level 2		Level 3

Assets:
Money market funds (included in cash and cash equivalents)	$	84,761	$	84,761	$	-	$	-
U.S. Treasury obligations ($223,032 included in cash and cash equivalents)	$	514,050	—		514,050		—
Corporate debt obligations ($46,714 included in cash and cash equivalents)	$	140,853	—		140,853		—
Federal agency obligations ($21,347 included in cash and cash equivalents)	$	41,891	—		41,891		—
Total fair value of assets	$	781,555	$	84,761	$	696,794	$	-


	Fair Value Measurements as of December 31, 2022
As of December 31, 2022:	Total		Level 1		Level 2		Level 3

Assets:
Money market funds (included in cash and cash equivalents)	$	238,223	$	238,223	$	-	$	-
U.S. Government bonds	25,459		-		25,459		-
U.S. Treasury bills	11,404		11,404		-		-
Corporate debt obligations	2,141		-		2,141		-
Federal agency obligations	8,506		-		8,506		-
Total fair value of assets	$	285,733	$	249,627	$	36,106	$	-

Liabilities:
Derivative tranche liability	$	10,291	$	-	$	-	$	10,291
Total fair value of liabilities	$	10,291	$	-	$	-	$	10,291


Classified as:	September 30, 2023		December 31, 2022
Cash and cash equivalents	$	374,862	$	238,223
Short-term marketable securities	406,693		47,510
Total cash equivalents and marketable securities	$	781,555	$	285,733

Summary of Changes in Level 3 Liabilities

The following table sets forth the changes in the fair value of Level 3 liabilities (in thousands):


	Derivative Tranche Liability
Balance as of December 31, 2022	$	10,291
Change in fair value	(10,291)
Balance as of September 30, 2023	$	—

Summary of Significant Assumptions Used to Estimate Fair Value

The following significant assumptions were used to estimate fair value of the derivative tranche liability as of December 31, 2022:


	December 31, 2022
Probability of achieving specified conditions	80		%
Fair value of Series C preferred stock share	$	12.2661
Discount rate	25		%

Commitments and Contingent Liabilities - Narrative (Details)	1 Months Ended		3 Months Ended	9 Months Ended
	Jul. 31, 2023 USD ($) ft²	Jan. 31, 2023 USD ($) ft²	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Square feet leased (in square feet) \| ft²		10,012
Term of contract		65 months
Renewal term		3 years
Monthly payments		$ 30,500
Annual rent increase		3.00%
Rent abatement, term		6 months
Security deposit			$ 34,000	$ 34,000
Operating lease liability, non-current		$ 1,300,000	1,252,000	1,252,000	$ 0
Operating lease, right-of-use asset		$ 1,300,000	1,240,000	1,240,000	$ 0
Office space leased (in square feet) \| ft²	22,365
Term of contract	60 months
Renewal term	3 years
Monthly payments	$ 150,000
Annual rent increase	3.50%
Operating lease costs (less than)			$ 100,000	$ 200,000
Weighted average remaining lease term			59 months	59 months
Discount rate			12.00%	12.00%
Lease liability measurement (less than)				$ 100,000

Description of Business, Organization and Liquidity (Details) $ / shares in Units, $ in Thousands				3 Months Ended						9 Months Ended
	May 09, 2023 USD ($) $ / shares shares	Apr. 25, 2023	Jan. 04, 2023 USD ($) shares	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Jul. 31, 2020 $ / shares
Subsidiary, Sale of Stock [Line Items]
Reverse stock split, conversion ratio		0.5071
Sale of stock, price (in dollars per share) \| $ / shares													$ 0.00002
Underwriting discounts, commissions and offering costs					$ 47,354
Temporary equity, convertible, conversion ratio	100.00%			100.00%						100.00%		1.00%
Net losses				$ 83,940	$ 26,039	$ 176,450	$ 14,406	$ 14,474	$ 16,085	$ 286,429	$ 44,965
Research and development				74,562			$ 12,509			272,512	38,222
Payments to acquire in-process research and development										10,000	0
Accumulated deficit				393,507						393,507		$ 107,078
Cash used in operating activities										96,074	$ 43,428
Cash, cash equivalents and short-term marketable securities				$ 788,400						788,400
Pierre Fabre
Subsidiary, Sale of Stock [Line Items]
Payments to acquire in-process research and development			$ 10,000							10,000
ValenzaBio Asset Acquisition
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares) \| shares			2,013,673
Research and development			$ 123,100							$ 123,100
ValenzaBio Asset Acquisition \| Common Class A
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares) \| shares			18,885,731
IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares) \| shares	34,500,000
Sale of stock, price (in dollars per share) \| $ / shares	$ 18.00
Gross proceeds received on transaction	$ 621,000
Net proceeds received on transaction	573,600
Underwriting discounts, commissions and offering costs	$ 47,400
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares) \| shares	4,500,000

Equity Incentive Plan - Narrative (Details) - USD ($)						1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
Equity Incentive Plan - Narrative (Details) - USD ($)	Aug. 16, 2023	May 09, 2023	May 04, 2023	Mar. 23, 2023	Jan. 04, 2023	Aug. 31, 2023	Apr. 30, 2023	Jul. 31, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, issued (in shares)									97,240,419		97,240,419		97,240,419
Common stock, outstanding (in shares)									2,767,359		2,767,359		2,767,359
Share-based and cash-based compensation, maximum			$ 750,000
Total shares reserved for future issuance (in shares)									20,726,850		20,726,850		48,458,034
Fair value of shares vested									$ 6,000,000.0		$ 7,800,000
Weighted-average grant date fair value, grants in period (in dollars per share)									$ 16.90		$ 13.69
Options granted (in shares)											4,771,615
Exercisable (in dollars per share)									$ 4.3478		$ 4.3478
Exercises in period (in shares)											40,570
Total stock-based compensation expense									$ 15,313,000	$ 560,000	$ 30,953,000	$ 2,539,000
Accrued compensation and other current liabilities									5,144,000		5,144,000		$ 4,237,000
Research and Development Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									3,572,000	364,000	8,661,000	862,000
General and Administrative Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									$ 11,741,000	196,000	$ 22,292,000	1,677,000
Nonemployee
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based and cash-based compensation, maximum			$ 1,000,000
Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period											10 years
Vesting period											4 years
Total shares reserved for future issuance (in shares)									8,704,462		8,704,462		5,036,946
Total stock-based compensation expense									$ 8,577,000	$ 560,000	$ 18,661,000	$ 1,234,000
Expected volatility										99.91%
Risk-free interest rate										3.05%
Expected dividend yield									0.00%	0.00%	0.00%	0.00%
ESPP Shares available for future grants
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Purchase price of common stock, Percent							85.00%
Total shares reserved for future issuance (in shares)									900,000		900,000		0
Number of shares authorized (in shares)							900,000
Percentage of eligible compensation for payroll deductions to purchase stock							15.00%
Annual increase, period							10 years
Annual increase as percentage of shares outstanding							1.00%
Maximum number of shares available over award term							2,700,000
Total stock-based compensation expense									$ 126,000	$ 0	$ 143,000	$ 0
Accrued compensation and other current liabilities									$ 300,000		$ 300,000
Unvested RSUs outstanding
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									2,183,413		2,183,413		1,107,213
Total stock-based compensation expense									$ 2,345,000	0	$ 7,884,000	0
Shares granted (in shares)	1,725,168												1,107,213
Accelerated vesting of awards (in shares)				138,401
Fair value				$ 8,000,000
Unvested RSUs outstanding \| Tranche One
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period											1 year
Unvested RSUs outstanding \| Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period											1 year
Unvested RSUs outstanding \| Tranche Three
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period											1 year
Unvested RSUs outstanding \| Tranche Four
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period											1 year
Unvested RSUs outstanding \| Chief Executive Officer
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense		$ 5,500,000
Vested (in shares)		640,416
Issued (in shares)		303,237
Withheld for tax withholding obligation (in shares)		337,179
Withheld for tax withholding obligation		$ 8,300,000
Shares unvested (in shares)		466,797
Performance-based restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period											3 years
Total shares reserved for future issuance (in shares)									2,988,492		2,988,492		0
Total stock-based compensation expense									$ 4,265,000	0	$ 4,265,000	0
Shares granted (in shares)											3,135,104
Vested (in shares)											0
Shares unvested (in shares)									2,988,492		2,988,492		0
Target number of shares (in shares)						3,135,104
Target number of shares, percentage						150.00%
Share price (in dollars per share)									$ 26.97		$ 26.97
Expected volatility											87.71%
Risk-free interest rate											4.47%
Expected dividend yield											0.00%
Granted (in dollars per share)											$ 27.43
Weighted-average recognition period											2 years 6 months
Unrecognized stock-based compensation expense									$ 77,700,000		$ 77,700,000
Unrecognized stock-based compensation expense, maximum									104,600,000		104,600,000
Restricted stock awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period								48 months
Total stock-based compensation expense									$ 0	$ 0	$ 0	$ 1,305,000
Vested (in shares)									88,743		266,229
Shares unvested (in shares)									295,803		295,803		562,032
2023 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock reserved for issuance (in shares)			12,000,000
Percentage of outstanding stock maximum			5.00%
Expiration period			10 years
Vesting period			4 years
Total shares reserved for future issuance (in shares)									4,661,603		4,661,603
2023 Equity Incentive Plan \| Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issuable (in shares)			56,762,538
2023 Equity Incentive Plan \| Stock options \| Stockholder, 10% or More
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period			5 years
2023 Equity Incentive Plan \| Stock options \| Minimum \| Stockholder, 10% or More
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Purchase price of common stock, Percent			110.00%
2020 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, issued (in shares)			6,920,846
Common stock, outstanding (in shares)			6,920,846
ValenaBio 2020 Stock Option Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options granted (in shares)					1,249,811
Exercisable (in dollars per share)					$ 3.6736
Exercises in period (in shares)									0		0
Unrecognized stock-based compensation expense									$ 63,200,000		$ 63,200,000
ValenaBio 2020 Stock Option Plan \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense											4,900,000
ValenaBio 2020 Stock Option Plan \| ValenzaBio Asset Acquisition \| Research and Development Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense											3,100,000
ValenaBio 2020 Stock Option Plan \| ValenzaBio Asset Acquisition \| General and Administrative Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense											$ 1,800,000
ValenaBio 2020 Stock Option Plan \| Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									1,249,811		1,249,811		0
Weighted-average recognition period											3 years 4 months 24 days
ValenaBio 2020 Stock Option Plan \| Stock options \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense					$ 4,900,000
ValenaBio 2020 Stock Option Plan \| Unvested RSUs outstanding
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized stock-based compensation expense									$ 46,400,000		$ 46,400,000
ValenaBio 2020 Stock Option Plan \| Restricted stock awards \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense					$ 900,000

Commitments and Contingent Liabilities - Summary of Maturity Analysis of Operating Lease Liability (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jan. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
2023 (remainder of the year)	$ 61
2024	375
2025	386
2026	398
2027	409
Thereafter	280
Total future lease payments	1,909
Less imputed interest	(476)
Total operating lease liability balance	1,433
Less current portion of lease liability (included in Accrued compensation and other current liabilities)	(181)
Operating lease liability, non-current	$ 1,252	$ 1,300	$ 0

Fair Value Measurements - Narrative (Details)	May 09, 2023 $ / shares	Dec. 31, 2022
Level 3 \| Fair value of Series C preferred stock share
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input	12.2661	12.2661
IPO
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Share price (in dollars per share)	$ 18.00

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net losses	$ (83,940)	$ (26,039)	$ (176,450)	$ (14,406)	$ (14,474)	$ (16,085)	$ (286,429)	$ (44,965)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Available-For-Sale Marketable Securities - Schedule of Available-for-Sale Marketable Securities (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	$ 781,605,000	$ 285,819,000
Total Unrealized Gains	60,000	0
Total Unrealized Loss	(110,000)	(86,000)
Total Estimated Fair Value	781,555,000	285,733,000
Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	374,862,000	238,223,000
Money market funds (included in cash and cash equivalents)
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	84,761,000	238,223,000
Total Unrealized Gains	0
Total Unrealized Loss	0	0
Total Estimated Fair Value	84,761,000	238,223,000
U.S. Government bonds
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost		25,506,000
Total Unrealized Loss		(47,000)
Total Estimated Fair Value		25,459,000
U.S. Treasury obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	514,029,000	11,430,000
Total Unrealized Gains	51,000
Total Unrealized Loss	(30,000)	(26,000)
Total Estimated Fair Value	514,050,000	11,404,000
U.S. Treasury obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	223,032,000
Corporate debt obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	140,923,000	2,145,000
Total Unrealized Gains	4,000
Total Unrealized Loss	(74,000)	(4,000)
Total Estimated Fair Value	140,853,000	2,141,000
Corporate debt obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	46,714,000
Federal agency obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	41,892,000	8,515,000
Total Unrealized Gains	5,000
Total Unrealized Loss	(6,000)	(9,000)
Total Estimated Fair Value	41,891,000	$ 8,506,000
Federal agency obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	$ 21,347,000

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 74,562	$ 12,509	$ 272,512	$ 38,222
General and administrative	19,861	2,887	44,440	8,145
Total operating expenses	94,423	15,396	316,952	46,367
Loss from operations	(94,423)	(15,396)	(316,952)	(46,367)
Change in fair value of derivative tranche liability	0	0	10,291	0
Interest income	10,502	986	20,486	1,399
Other expense, net	(19)	4	(254)	3
Net loss	(83,940)	(14,406)	(286,429)	(44,965)
Other comprehensive gain (loss)
Unrealized gain (loss) on short-term marketable securities, net	(94)	(62)	36	(200)
Total other comprehensive gain (loss)	(94)	(62)	36	(200)
Net loss and other comprehensive loss	$ (84,034)	$ (14,468)	$ (286,393)	$ (45,165)
Net loss per share attributable to common stockholder, basic (in shares)	$ (0.87)	$ (8.17)	$ (4.68)	$ (31.66)
Net loss per share attributable to common stockholder, diluted (in shares)	$ (0.87)	$ (8.17)	$ (4.68)	$ (31.66)
Weighted-average common shares outstanding, basic (in shares)	96,872,747	1,764,293	61,138,105	1,420,199
Weighted-average common shares outstanding, diluted (in shares)	96,872,747	1,764,293	61,138,105	1,420,199

Fair Value Measurements - Schedule of Financial Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Sep. 09, 2022
Assets:
Debt securities, available-for-sale	$ 781,555	$ 285,733
Total fair value of assets	781,555	285,733
Liabilities:
Derivative tranche liability		10,291	$ 10,778	$ 10,800
Total fair value of liabilities		10,291
Cash and cash equivalents
Assets:
Debt securities, available-for-sale	374,862	238,223
Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	84,761	238,223
U.S. Government bonds
Assets:
Debt securities, available-for-sale		25,459
U.S. Treasury bills
Assets:
Debt securities, available-for-sale	514,050	11,404
U.S. Treasury bills \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	223,032
Corporate debt obligations
Assets:
Debt securities, available-for-sale	140,853	2,141
Corporate debt obligations \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	46,714
Federal agency obligations
Assets:
Debt securities, available-for-sale	41,891	8,506
Federal agency obligations \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	21,347
Level 1
Assets:
Total fair value of assets	84,761	249,627
Liabilities:
Derivative tranche liability		0
Total fair value of liabilities		0
Level 1 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	84,761	238,223
Level 1 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		0
Level 1 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	0	11,404
Level 1 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	0	0
Level 1 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	0	0
Level 2
Assets:
Total fair value of assets	696,794	36,106
Liabilities:
Derivative tranche liability		0
Total fair value of liabilities		0
Level 2 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	0	0
Level 2 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		25,459
Level 2 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	514,050	0
Level 2 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	140,853	2,141
Level 2 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	41,891	8,506
Level 3
Assets:
Total fair value of assets	0	0
Liabilities:
Derivative tranche liability		10,291
Total fair value of liabilities		10,291
Level 3 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		0
Level 3 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	$ 0	$ 0

Consolidated Balance Sheet Components

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Consolidated Balance Sheet Components

Prepaid expenses and other current assets

Prepaid expenses and other current assets consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Prepaid insurance and other current assets	$	1,834	$	86
Prepaid research and development expenses	1,645		682
VAT receivable	1,292		—
Prepaid other services	776		288
Interest receivable	660		138
Research and development credit receivable	-		250
Total	$	6,207	$	1,444

Prepaid expenses and other assets, non-current

Other non-current assets consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Prepaid research and development expenses, non-current	$	2,448	$	1,964
Security deposits	34		—
Deferred IPO offering costs	—		774
Acquisition transaction costs	-		1,121
Total	$	2,482	$	3,859

Property, plant and equipment

Property, plant and equipment consisted of the following as of September 30, 2023 (in thousands):


	September 30, 2023
Construction in progress	$	1,499
Furniture and fixtures	263
Computer and other equipment	344
Leasehold improvements	90
Total property, plant and equipment, gross	2,196
Less: accumulated depreciation and amortization	(67)
Property, plant and equipment, net	$	2,129

There was no property, plant and equipment balance as of December 31, 2022.

Accrued compensation and other current liabilities

Accrued compensation and other current liabilities consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued compensation	$	4,016	$	3,068
Accrued professional services fees (1)	751		808
Other accrued expenses and current liabilities	377		361
Total	$	5,144	$	4,237

(1)IPO offering costs included in accrued liabilities were zero and $0.2 million as of September 30, 2023 and December 31, 2022, respectively.

Net Loss Per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Numerator:
Net loss	$	(83,940)	$	(14,406)	$	(286,429)	$	(44,965)
Denominator:
Weighted average common shares outstanding	97,227,070		3,358,972		61,580,296		3,268,666
Less: Weighted-average common shares subject to repurchase	(354,323)		(1,594,679)		(442,191)		(1,848,467)
Weighted-average common shares outstanding, basic and diluted	96,872,747		1,764,293		61,138,105		1,420,199
Net loss per share attributable to common stockholders, basic and diluted	$	(0.87)	$	(8.17)	$	(4.68)	$	(31.66)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share


	As of September 30,
	2023	2022
Outstanding options to purchase common stock	8,704,462	2,598,180
Unvested RSUs outstanding	2,183,413	451,247
Outstanding options to purchase common stock assumed upon the ValenzaBio acquisition	1,249,811	0
Common stock subject to repurchase	295,803	1,477,641
Redeemable convertible preferred stock	0	40,743,522
Total	12,433,489	45,270,590

Equity Incentive Plan - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 15,313	$ 560	$ 30,953	$ 2,539
Restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	2,345	0	7,884	0
Performance-based restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	4,265	0	4,265	0
Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	8,577	560	18,661	1,234
ESPP
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	126	0	143	0
Restricted stock awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	0	0	0	1,305
General and administrative expenses
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	11,741	196	22,292	1,677
Research and development expenses
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 3,572	$ 364	$ 8,661	$ 862

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Section 50
-Paragraph 2
-Subparagraph (a)(2)
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Net Loss Per Share Attributable to Common Stockholders - Schedule of Outstanding Shares Of Potentially Dilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	12,433,489	45,270,590
Outstanding options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	8,704,462	2,598,180
Outstanding options to purchase common stock \| ValenzaBio Asset Acquisition
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,249,811	0
Unvested RSUs outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,183,413	451,247
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	295,803	1,477,641
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	40,743,522

Significant Agreements (Details) - USD ($)				3 Months Ended		9 Months Ended		12 Months Ended
Significant Agreements (Details) - USD ($)	Jan. 04, 2023	Aug. 09, 2021	Mar. 25, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021	Dec. 31, 2022	Oct. 31, 2021	Sep. 30, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development				$ 74,562,000	$ 12,509,000	$ 272,512,000	$ 38,222,000
Affibody \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments										$ 22,000,000	$ 3,000,000
Maximum aggregate milestone payments		$ 280,000,000
Payment due prior to milestone		$ 30,000,000
Aggregate milestone payments, period		10 years
Contingent payments, percentage		33.33%
Fair value threshold percentage		33.33%
Probable milestone payments				0		0			$ 0
Research and development								$ 25,000,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments			$ 10,000,000
Aggregate milestone payments, period			10 years
Termination period			9 months
Probable milestone payments				0		0
Research and development						10,000,000
One-time payment			$ 31,000,000
One-time payment, period			30 days
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Development and Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments			$ 99,500,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Commercial Sales Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments			$ 390,000,000
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments, period	10 years
Probable milestone payments				$ 0		$ 0
Contract termination, period	30 days
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Development and Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments	$ 44,300,000
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Commercial Sales Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments	$ 682,000,000