Annexon (ANNX) 10-K 3 Mar 25 2024 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Feb. 26, 2025	Jun. 28, 2024
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Dec. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Trading Symbol	ANNX
Entity Registrant Name	ANNEXON, INC.
Entity Central Index Key	0001528115
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-39402
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-5414423
Entity Address, Address Line One	1400 Sierra Point Parkway
Entity Address, Address Line Two	Bldg C
Entity Address, Address Line Three	Suite 200
Entity Address, City or Town	Brisbane
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94005
City Area Code	650
Local Phone Number	822-5500
Entity Small Business	true
Entity Emerging Growth Company	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 477.2
ICFR Auditor Attestation Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Auditor Name	KPMG LLP
Auditor Location	San Francisco, CA
Auditor Firm ID	185
Common Stock [Member]
Entity Common Stock, Shares Outstanding		109,709,826
Prefunded Warrant [Member]
Entity Common Stock, Shares Outstanding		38,543,577

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 49,498	$ 225,110
Short-term investments	262,519	34,606
Prepaid expenses and other current assets	4,444	4,144
Total current assets	316,461	263,860
Restricted cash	1,032	1,032
Property and equipment, net	12,638	14,773
Operating lease right-of-use assets	16,705	18,009
Other non-current assets	3,235
Total assets	350,071	297,674
Current liabilities:
Accounts payable	10,426	5,487
Accrued and other current liabilities	17,568	10,276
Operating lease liabilities, current	2,518	2,165
Total current liabilities	30,512	17,928
Operating lease liabilities, non-current	26,454	29,190
Total liabilities	56,966	47,118
Commitments and contingencies (Note 5)
Stockholders’ equity:
Common stock, $0.001 par value; 300,000,000 shares authorized as of December 31, 2024 and 2023; 109,381,556 and 78,369,099 shares issued and outstanding as of December 31, 2024 and 2023, respectively	109	78
Additional paid-in capital	1,003,685	823,029
Accumulated other comprehensive income (loss)	10	(52)
Accumulated deficit	(710,699)	(572,499)
Total stockholders' equity	293,105	250,556
Total liabilities and stockholders’ equity	$ 350,071	$ 297,674

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	109,381,556	78,369,099
Common stock, shares outstanding	109,381,556	78,369,099

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating expenses:
Research and development	$ 119,448	$ 113,756
General and administrative	34,625	29,967
Total operating expenses	154,073	143,723
Loss from operations	(154,073)	(143,723)
Interest and other income, net	15,873	9,486
Net loss	$ (138,200)	$ (134,237)
Net loss per share, basic	$ (1.01)	$ (1.77)
Net loss per share, diluted	$ (1.01)	$ (1.77)
Weighted-average shares used in computing net loss per share, basic	137,404,145	75,673,081
Weighted-average shares used in computing net loss per share, diluted	137,404,145	75,673,081

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (138,200)	$ (134,237)
Other comprehensive income (loss):
Foreign currency translation adjustment	(15)	5
Unrealized gain on available-for-sale securities	77	315
Comprehensive loss	$ (138,138)	$ (133,917)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Related Party [Member]	Common Stock [Member]	Common Stock [Member] Related Party [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Related Party [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning Balance, Values at Dec. 31, 2022	$ 231,194		$ 48		$ 669,780		$ (372)	$ (438,262)
Beginning Balance, Shares at Dec. 31, 2022			47,722,995
Exercise of stock options, Value	145				145
Exercise of stock options, Shares			76,888
Exercise of pre-funded warrants, Value			$ 3		(3)
Exercise of pre-funded warrants, Shares			2,582,557
Issuance of common stock, net of issuance costs, Value		$ 17,470		$ 2		$ 17,468
Issuance of common stock, net of issuance costs, Shares				2,646,458
Issuance of common stock and pre-funded warrants, net of issuance costs, Value	117,002		$ 25		116,977
Issuance of common stock and pre-funded warrants, net of issuance costs, Shares			25,035,000
Issuance of common stock per Employee Stock Purchase Plan purchase, Value	479				479
Issuance of common stock per Employee Stock Purchase Plan purchase, Shares			133,105
Restricted stock vested in the period, Shares			172,096
Stock-based compensation, Value	18,183				18,183
Other comprehensive income, Value	320						320
Net loss	(134,237)							(134,237)
Ending Balance, Values at Dec. 31, 2023	250,556		$ 78		823,029		(52)	(572,499)
Ending Balance, Shares at Dec. 31, 2023			78,369,099
Exercise of stock options, Value	$ 1,232				1,232
Exercise of stock options, Shares	382,122		382,122
Exercise of pre-funded warrants, Value			$ 9		(9)
Exercise of pre-funded warrants, Shares			8,947,923
Exercise of common warrants, Shares			19,901
Issuance of common stock, net of issuance costs, Value	$ 42,843		$ 8		42,835
Issuance of common stock, net of issuance costs, Shares			8,326,067
Issuance of common stock and pre-funded warrants, net of issuance costs, Value	116,817		$ 13		116,804
Issuance of common stock and pre-funded warrants, net of issuance costs, Shares			13,001,120
Issuance of common stock per Employee Stock Purchase Plan purchase, Value	362		$ 1		361
Issuance of common stock per Employee Stock Purchase Plan purchase, Shares			138,147
Restricted stock vested in the period, Shares			197,177
Stock-based compensation, Value	19,433				19,433
Other comprehensive income, Value	62						62
Net loss	(138,200)							(138,200)
Ending Balance, Values at Dec. 31, 2024	$ 293,105		$ 109		$ 1,003,685		$ 10	$ (710,699)
Ending Balance, Shares at Dec. 31, 2024			109,381,556

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Stock issuance costs	$ 1,528
Related Party [Member]
Stock issuance costs		$ 525
Common Stock and Prefunded Warrants [Member]
Stock issuance costs	$ 8,183	$ 8,014

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating activities:
Net loss	$ (138,200)	$ (134,237)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,150	2,148
Accretion of discount on available-for-sale securities	(9,054)	(2,550)
Stock-based compensation	19,433	18,183
Reduction in the carrying amount of right-of-use assets	1,304	1,119
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(300)	1,352
Other non-current assets	(3,184)
Accounts payable	4,936	(2,077)
Accrued and other current liabilities	7,292	(3,577)
Operating lease liabilities	(2,383)	(1,503)
Net cash used in operating activities	(118,006)	(121,142)
Investing activities:
Purchases of property and equipment	(15)	(193)
Purchases of available-for-sale securities	(583,932)	(108,088)
Proceeds from maturities of available-for-sale securities	365,150	178,984
Net cash (used in) provided by investing activities	(218,797)	70,703
Financing activities:
Proceeds from the exercise of common stock options	1,232	90
Proceeds from Employee Stock Purchase Plan purchases	362	479
Proceeds from the issuance of common stock, including to related parties, of zero and $17,995 for the years ended December 31, 2024 and 2023, respectively	44,371	17,995
Proceeds from the issuance of common stock and pre-funded warrants, net of commissions	117,500	117,515
Payment of financing costs	(2,259)	(555)
Net cash provided by financing activities	161,206	135,524
(Decrease) increase in cash, cash equivalents and restricted cash	(175,597)	85,085
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(15)	5
Cash, cash equivalents and restricted cash
Beginning of period	226,142	141,052
End of period	50,530	226,142
Supplemental disclosure of cash flow information:
Cash paid for amounts included in the measurement of lease liability	4,893	4,728
Non-cash investing and financing activities:
Deferred offering costs included in accounts payable and accrued liabilities	3	$ 483
Deferred offering costs included in other non-current assets	$ 51

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from the issuance of common stock including related party	$ 0	$ 17,995

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (138,200)	$ (134,237)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2024 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	Trading Arrangements of Section 16 Reporting Persons. During the Company’s last fiscal quarter, the Company’s directors and officers (as defined in Rule 16a-1(f) under the Exchange Act) 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. Types of Trading Arrangement Name and Position Action Termination Date Rule Non-Rule 10b5-1** Total Shares of Common Stock to be Sold Total Shares of Common Stock to be Purchased Expiration Date Douglas Love , Chief Executive Officer Terminate 12/16/2024 X 37,994 1/22/2025 __________________ * 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(a) of Regulation S-K under the Exchange Act.
Douglas Love [Member]
Trading Arrangements, by Individual
Name	Douglas Love
Title	Chief Executive Officer
Rule 10b5-1 Arrangement Terminated	true
Termination Date	12/16/2024
Expiration Date	1/22/2025
Aggregate Available	37,994

Cybersecurity Risk Management,

Cybersecurity Risk Management, Strategy, and Governance Disclosure	12 Months Ended
	Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	Item 1C. Cybersecurity Risk management and strategy We have implemented a risk-based approach designed to identify, assess and manage cybersecurity threats that could materially affect our business and information systems. We attempt to identify and assess risks from cybersecurity threats by evaluating our threat environment using various methods including, for example: maintaining manual and automated tools, subscribing to reports and services that identify cybersecurity threats, evaluating threats reported to us, and completing third-party cybersecurity threat assessments. We use cybersecurity consultants and penetration testing firms in an effort to identify, assess, and manage material risks from cybersecurity threats. We use third-party service providers in various elements to our business operations such as data hosting providers. To help manage cybersecurity risks associated with our use of third-party service providers, we primarily engage with industry-preferred service providers, and we also contractually require service providers with access to personal, confidential, or proprietary information to maintain data security controls and practices. For a description of the risks from cybersecurity threats that may materially affect the Company and how they may do so, see our risk factors under Part 1. Item 1A. Risk Factors in this Annual Report on Form 10-K, including “ Cybersecurity risks and the failure to maintain the security, confidentiality, integrity, or availability of our information technology systems or data, and those maintained on our behalf, could lead to adverse consequences that materially adversely affect our business, including, without limitation, regulatory investigations or actions, a material interruption to our operations, including clinical trials, damage to our reputation and/or subject us to costs, loss of customers or sales, fines and penalties or lawsuits. ” Governance Our board of directors addresses our cybersecurity risk management as part of its general oversight function. The audit committee is responsible for advising on our cybersecurity risk management processes, including oversight of mitigation of risks from cybersecurity threats. Our cybersecurity risk assessment and risk management processes are managed by certain members of our management, including our CFO (who has prior experience in strategic business operations). Our CFO has supervisory responsibility over IT and cybersecurity functions. Our management is responsible for helping to integrate cybersecurity risk considerations into our overall risk management strategy, helping prepare for and respond to cybersecurity incidents, and reviewing security assessments and other security-related reports . Our incident response team is responsible for remediating cybersecurity incidents of which they are notified. We maintain a cybersecurity policy, reviewed with our audit committee, which is designed to address cybersecurity risks to us (including by escalating certain cybersecurity incidents to members of management and the board of the audit committee, in each case depending on the circumstances). We also maintain incident response procedures designed to assist us in responding to cybersecurity incidents.
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	Our cybersecurity risk assessment and risk management processes are managed by certain members of our management, including our CFO (who has prior experience in strategic business operations). Our CFO has supervisory responsibility over IT and cybersecurity functions. Our management is responsible for helping to integrate cybersecurity risk considerations into our overall risk management strategy, helping prepare for and respond to cybersecurity incidents, and reviewing security assessments and other security-related reports . Our incident response team is responsible for remediating cybersecurity incidents of which they are notified.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	Our board of directors addresses our cybersecurity risk management as part of its general oversight function. The audit committee is responsible for advising on our cybersecurity risk management processes, including oversight of mitigation of risks from cybersecurity threats.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	Our board of directors addresses our cybersecurity risk management as part of its general oversight function.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	Our CFO has supervisory responsibility over IT and cybersecurity functions. Our management is responsible for helping to integrate cybersecurity risk considerations into our overall risk management strategy, helping prepare for and respond to cybersecurity incidents, and reviewing security assessments and other security-related reports . Our incident response team is responsible for remediating cybersecurity incidents of which they are notified.
Cybersecurity Risk Role of Management [Text Block]	Our cybersecurity risk assessment and risk management processes are managed by certain members of our management, including our CFO (who has prior experience in strategic business operations). Our CFO has supervisory responsibility over IT and cybersecurity functions. Our management is responsible for helping to integrate cybersecurity risk considerations into our overall risk management strategy, helping prepare for and respond to cybersecurity incidents, and reviewing security assessments and other security-related reports . Our incident response team is responsible for remediating cybersecurity incidents of which they are notified. We maintain a cybersecurity policy, reviewed with our audit committee, which is designed to address cybersecurity risks to us (including by escalating certain cybersecurity incidents to members of management and the board of the audit committee, in each case depending on the circumstances). We also maintain incident response procedures designed to assist us in responding to cybersecurity incidents.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	The audit committee is responsible for advising on our cybersecurity risk management processes, including oversight of mitigation of risks from cybersecurity threats.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	Our cybersecurity risk assessment and risk management processes are managed by certain members of our management, including our CFO (who has prior experience in strategic business operations).
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	Our incident response team is responsible for remediating cybersecurity incidents of which they are notified.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

Organization

Organization	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Organization	1. Organization Annexon, Inc., or the Company, is a clinical-stage biopharmaceutical company pioneering a new class of complement medicines for people living with devasting inflammatory-related diseases. The Company is located in Brisbane, California and was incorporated in Delaware in March 2011. The Company’s wholly-owned subsidiary, Annexon Biosciences Australia Pty Ltd, or the Subsidiary, is a proprietary limited company incorporated in 2016 and domiciled in Australia. Liquidity Since inception, the Company has been involved primarily in performing research and development activities, conducting clinical trials, hiring personnel, and raising capital to support and expand these activities. The Company has experienced losses and negative cash flows from operations since its inception and, as of December 31, 2024, had an accumulated deficit of $ 710.7 million and cash and cash equivalents and short-term investments of $ 312.0 million. The Company has historically funded its operations through the issuance of shares of its common stock and warrants. Based on projected activities, management projects that existing cash and cash equivalents and short-term investments will enable the Company to fund its operating expenses and capital expenditure requirements for at least twelve months from the date of issuance of these financial statements. The Company’s future viability beyond that point is dependent on its ability to achieve development milestones and obtain additional funding. Management expects to continue to incur losses and negative cash flows from operations for at least the next several years. There are uncertainties associated with the Company’s ability to (1) obtain additional equity or debt financing on terms that are favorable to the Company, (2) enter into collaborative agreements with strategic partners, and (3) succeed in its future operations. If the Company is not able to obtain the required funding for its operations or is not able to obtain funding on terms that are favorable to the Company, it could be forced to delay, reduce or eliminate its research and development programs and its business could be materially harmed.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	2. Basis of Presentation and Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. Management evaluates its estimates, including but not limited to the fair value of investments, operating lease right-of-use assets and liabilities, valuation of deferred tax assets and uncertain tax positions (including valuation allowance), clinical trial accruals and stock-based compensation. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Principles of Consolidation The consolidated financial statements include the operations of Annexon, Inc. and its wholly owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation. Segments The Company’s chief operating decision maker ("CODM") is its Chief Executive Officer. The CODM reviews financial information on an aggregate basis for the purposes of evaluating financial performance and allocating the Company’s resources. Accordingly, the Company has determined that it operates in one segment. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid instruments with an original maturity of three months or less at time of purchase to be cash equivalents. Cash equivalents, which includes amounts invested in money market funds and short-term government bonds, are stated at fair value. Restricted cash as of December 31, 2024 relates to the letters of credit established for the Company’s office lease. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows (in thousands): December 31, 2024 2023 Cash $ 2,651 $ 8,488 Cash equivalents 46,847 216,622 Cash and cash equivalents 49,498 225,110 Restricted cash 1,032 1,032 Cash, cash equivalents and restricted cash $ 50,530 $ 226,142 Short-Term Investments Short-term investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. The Company determines the appropriate classification of its investments in debt securities at the time of purchase. Available-for-sale securities with original maturities beyond three months at the date of purchase are classified as current based on their availability for use in current operations. The Company evaluates, on a quarterly basis, its available-for-sale debt securities for potential impairment. For available-for-sale debt securities in an unrealized loss position, the Company assesses whether such declines are due to credit loss based on factors such as changes to the rating of the security by a ratings agency, market conditions and supportable forecasts of economic and market conditions, among others. If credit loss exists, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale debt security before recovery of its amortized cost basis. If either condition is met, the security’s amortized cost basis is written down to fair value and is recognized through interest and other income (expense), net. If neither condition is met, declines as a result of credit losses, if any, are recognized as an allowance for credit loss, limited to the amount of unrealized loss, through interest and other income (expense), net. Any portion of the unrealized loss that is not a result of a credit loss, is recognized in other comprehensive income (loss). Realized gains and losses, if any, on available-for-sale debt securities are included in interest and other income (expense), net. The cost of investments sold is based on the specific-identification method. Interest on available-for-sale debt securities is included in interest and other income (expense), net. Property and Equipment, Net Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. The useful lives of the property and equipment are as follows: Computer equipment 3 years Lab equipment and furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. When indications of impairment are present and the estimated undiscounted future cash flows from the use of these assets is less than the assets’ carrying value, the related assets will be written down to fair value. There were no impairments of the Company’s long-lived assets for the periods presented. Leases The Company determines if an arrangement is a lease at inception. The Company includes operating leases in operating lease right of use, or ROU, assets, current and noncurrent operating lease liabilities in the Company’s consolidated balance sheets. The ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The Company measures the ROU assets based on the associated lease liabilities adjusted for any lease incentives such as tenant improvement allowances. As most of the leases do not provide an implicit rate, the Company generally uses its incremental borrowing rate based on the estimated rate of interest for collateralized borrowing over a similar term of the lease payments at the commencement date. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise the option. Lease expense for lease payments is recognized on a straight-line basis, net of sublease income, over the lease term. As a practical expedient, the Company elected, for all facility leases, not to separate non-lease components from lease components and instead to account for each separate lease component and its associated non-lease components as a single lease component. The Company elected to exclude from its balance sheets recognition of leases having a term of 12 months or less (short-term leases). Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Valuation allowances are established when necessary to reduce deferred taxes to the amounts expected to be realized. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merit, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Commitments and Contingencies Liabilities for loss contingencies arising from claims, assessments, litigation, fines, and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred. Warrants Warrants are accounted for as either derivative liabilities or as equity instruments depending on the specific terms of the agreement. The Company’s pre-funded and common warrants are equity-classified instruments that were recorded in additional paid-in capital at issuance and are not subject to remeasurement. The Company periodically evaluates changes in facts and circumstances that could impact the classification of warrants. Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials and commercial materials to support future biologics license applications ("BLA") to the FDA, and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. The Company also estimates manufacturing costs based on services performed pursuant to contracts with contract manufacturing organizations that develop and manufacture product on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust the accrual accordingly to reflect the best information available at the time of the financial statement issuance. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception. Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees and non-employee directors and consultants using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options and restricted stock units, or RSUs. The fair value method requires the Company to estimate the fair value of stock options to employees and non-employees on the date of grant using the Black-Scholes option pricing model. The fair value of RSU awards is based on the fair value of the underlying common stock as of the grant date. Stock-based compensation costs are based on the fair value of the underlying RSUs and options and recognized as expense on a straight-line basis over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures as they occur. Net Loss Per Share Basic net loss per share attributable to common stockholders is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share because the effects of potentially dilutive securities are antidilutive. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. The Company’s cash and cash equivalents and short-term investments are held by high credit quality financial institutions in the United States. At times, such deposits may be in excess of the Federal Depository Insurance Corporation insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions. Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (ASU) 2023-07, Segment Reporting: Improvements to Reportable Segment Disclosures , which requires disclosure of incremental segment information on an interim and annual basis. This ASU is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal periods beginning after December 15, 2024, and requires retrospective application to all prior periods presented in the financial statements. The Company adopted annual and interim requirements under ASU 2023-07 on January 1, 2024 and 2025, respectively. The adoption of ASU 2023-07 did no t have a material impact on the Company's consolidated financial statements. See Note 10 — Segment Reporting. Recently Issued Accounting Pronouncements In December 2023, the FASB issued ASU 2023-09, Income Taxes: Improvements to Income Tax Disclosures , which requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures : Disaggregation of Income Statement Expenses , which requires public entities to disclose additional information about specific expense categories in the notes to the financial statements on an interim and annual basis. This guidance is effective for annual reporting periods beginning after December 15, 2026, and interim periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines fair value based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: • Level 1 Inputs: Unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date. • Level 2 Inputs: Other than quoted prices included in Level 1 inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability. • Level 3 Inputs: Unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at measurement date. On a recurring basis, the Company measures certain financial assets and liabilities at fair value. The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2024 Valuation Amortized Gross Gross Aggregate Assets: Cash equivalents: Money market funds Level 1 $ 31,680 $ — $ — $ 31,680 Government bonds Level 2 15,167 — — 15,167 Total cash equivalents 46,847 — — 46,847 Short-term investments: Government bonds Level 2 262,424 98 ( 3 ) 262,519 Total short-term investments 262,424 98 ( 3 ) 262,519 $ 309,271 $ 98 $ ( 3 ) $ 309,366 December 31, 2023 Valuation Amortized Gross Gross Aggregate Assets: Cash equivalents: Money market funds Level 1 $ 143,933 $ — $ — $ 143,933 Government bonds Level 2 72,689 — — 72,689 Total cash equivalents 216,622 — — 216,622 Short-term investments: Government bonds Level 2 34,596 10 — 34,606 Total short-term investments 34,596 10 — 34,606 $ 251,218 $ 10 $ — $ 251,228 All of the investments held as of December 31, 2024 had original maturities of less than two years . As of December 31, 2024, all of the investments are scheduled to mature in 12 months . During the year ended December 31, 2024, the Company did no t recognize any credit losses. The Company determined that the decline in fair value of debt securities was not due to credit-related factors, and no allowance for expected credit losses was recorded as of December 31, 2024. There were nominal unrealized losses as of December 31, 2024, and no unrealized losses have been in the loss position for more than 12 months. However, the Company is planning to hold these securities until maturity and expects to recover the amortized cost basis. For the years ended December 31, 2024 and 2023, the Company recognized no material realized gains or losses on financial instruments.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2024
Disclosure Of Balance Sheet Components [Abstract]
Balance Sheet Components	4. Balance Sheet Components Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2024 2023 Prepaid research and development costs $ 2,640 $ 2,617 Prepaid insurance 700 704 Prepaid and other current assets 1,104 823 Total prepaid expenses and other current assets $ 4,444 $ 4,144 Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2024 2023 Leasehold improvements $ 17,254 $ 17,245 Laboratory equipment 1,838 1,832 Furniture and fixtures 692 692 Computer equipment and software 33 33 Total property and equipment, gross 19,817 19,802 Less: accumulated depreciation ( 7,179 ) ( 5,029 ) Total property and equipment, net $ 12,638 $ 14,773 Total depreciation expense recognized for the years ended December 31, 2024 and 2023 was $ 2.2 million and $ 2.1 million, respectively. Accrued and Other Current Liabilities Accrued and other current liabilities consisted of the following (in thousands): December 31, 2024 2023 Accrued research and development expenses $ 10,992 $ 4,027 Accrued compensation 5,833 5,607 Accrued professional services 602 501 Other accrued and current liabilities 141 141 Total accrued and other current liabilities $ 17,568 $ 10,276

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies Leases The Company leases its offices and laboratory in Brisbane, California, or the Brisbane Lease, under a ten-year noncancelable lease agreement that ends in October 2031 with a ten-year renewable option. In November 2021, the Company subleased unoccupied space for two years from December 2021 through November 2023 , for aggregate sublease payments of $ 3.4 million. The sublease income, while it reduces the rent expense, is not considered in the value of the right-of-use assets or lease liabilities. The Company’s sublease income was zero and $ 2.0 million for the years ended December 31, 2024 and 2023, respectively. As of December 31, 2024, the operating lease right-of-use assets were $ 16.7 million and lease liabilities were $ 29.0 million in the consolidated balance sheet. The weighted average remaining lease term is 6.8 years. The weighted average incremental borrowing rate used to measure the operating lease liability is 8.4 % . Operating lease cost for the years ended December 31, 2024 and 2023 was $ 3.8 million and $ 2.3 million, respectively. Variable lease payments for the years ended December 31, 2024 and 2023 were $ 2.3 million and $ 1.5 million, respectively. Future minimum lease payments and related lease liabilities as of December 31, 2024 were as follows: (in thousands) 2025 $ 5,065 2026 5,242 2027 5,425 2028 5,615 2029 and thereafter 16,985 Total undiscounted lease payments 38,332 Less: Imputed interest ( 9,360 ) Total $ 28,972 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. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has no t paid any claims or been required to defend any action related to its indemnification obligations. As of December 31, 2024, the Company did no t have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

Stockholder's Equity

Stockholder's Equity	12 Months Ended
	Dec. 31, 2024
Stockholders' Equity Note [Abstract]
Stockholder's Equity	6. Stockholders' Equity 2024 Financing In June 2024, the Company raised net proceeds of approximately $ 116.8 million after deducting underwriting discounts and offering expenses through the sale of 13,001,120 shares of the Company’s common stock, par value $ 0.001 per share at a price of $ 6.25 per share and pre-funded warrants to purchase an aggregate of 7,000,000 shares of common stock at a price of $ 6.249 per share, which equals the per share offering price for the shares of common stock less the $ 0.001 exercise price for each pre-funded warrant. The pre-funded warrants are immediately exercisable, subject to certain beneficial ownership limitations. The warrants meet the criteria for equity classification and were therefore recorded at fair value as of the grant date as a component of stockholders’ equity within additional paid-in capital. 2023 Financing In December 2023, the Company raised net proceeds of approximately $ 117.0 million after deducting underwriting discounts and offering expenses through the sale of 25,035,000 shares of the Company’s common stock, par value $ 0.001 per share at a price of $ 2.880 per share and pre-funded warrants to purchase an aggregate of 18,379,861 shares of common stock at a price of $ 2.879 per share, which equals the per share offering price for the shares of common stock less the $ 0.001 exercise price for each pre-funded warrant. An entity related to one of the Company’s directors participated in the public offering and purchased 350,000 shares of common stock for an aggregate price of approximately $ 1.0 million. The warrants meet the criteria for equity classification and were therefore recorded at fair value as of the grant date as a component of stockholders’ equity within additional paid-in capital. The Company issued an aggregate of 5,243,400 shares and 965,427 shares of common stock upon the cashless and cash exercise of these pre-funded warrants in February 2024 and April 2024, respectively. 2022 Financing In July 2022, the Company raised net proceeds of approximately $ 122.5 million after deducting fees and expenses through the sale of an aggregate of 9,013,834 shares of common stock, pre-funded warrants to purchase up to 24,696,206 shares of its common stock and accompanying common warrants to purchase up to 8,427,508 shares of its common stock. The offering price per share and accompanying common warrant was $ 3.87125 per share and the offering price per pre-funded warrant and accompanying common warrant was $ 3.87025 per share, which equals the per share offering price for the shares of common stock less the $ 0.001 exercise price for each such pre-funded warrant. The pre-funded warrants remain exercisable until exercised in full. The common warrants have an exercise price of $ 5.806875 per share and expire on June 30, 2025 . Both the pre-funded and common warrants are immediately exercisable, subject to beneficial ownership limitations. The warrants meet the criteria for equity classification and were therefore recorded at fair value as of the grant date as a component of stockholders’ equity within additional paid-in capital. The Company issued an aggregate of 2,582,557 shares of common stock upon the cashless exercise of the pre-funded warrants in March 2023. The Company issued an aggregate of 19,901 and 2,739,096 shares of common stock upon the cashless exercise of the common warrants and pre-funded warrants in June 2024 and November 2024, respectively. Pre-Funded and Common Warrants The following summarizes warrant activity during the years ended December 31, 2024 and 2023: Number of Common Warrants Number of Pre-funded Warrants Weighted-Average Exercise Price Balances as of December 31, 2022 8,427,508 24,696,206 Issued — 18,379,861 $ 0.001 Exercised — ( 2,583,144 ) $ 0.001 Balances as of December 31, 2023 8,427,508 40,492,923 Issued — 7,000,000 $ 0.001 Exercised ( 322,893 ) ( 8,949,346 ) $ 0.216 Balances as of December 31, 2024 8,104,615 38,543,577 2024 At-the-Market ("ATM") Program In March 2024, the Company entered into a sales agreement with TD Cowen, as sales agent, or 2024 ATM program, pursuant to which the Company may issue and sell shares of its common stock for an aggregate maximum offering of $ 100.0 million. TD Cowen is entitled to compensation up to 3 % of the aggregate gross proceeds for the common stock sold through the 2024 ATM program. During the year ended December 31, 2024, t he Company sold 750,000 shares of common stock for net proceeds of approximately $ 4.5 million, after deducting commissions paid to TD Cowen. As of December 31, 2024, approximately $ 95.4 million remained available for the offer and sales of shares of common stock under the 2024 ATM program. 2021 ATM Program In August 2021, the Company entered into a sales agreement with TD Cowen as sales agent, pursuant to which the Company may issue and sell shares of its common stock for an aggregate maximum offering of $ 100.0 million under an at-the-market offering program, or 2021 ATM program. TD Cowen is entitled to compensation up to 3 % of the aggregate gross proceeds for the common stock sold through the 2021 ATM program. During the years ended December 31, 2024 and 2023, the Company sold 7,576,067 shares and 2,646,458 shares of common stock, respectively, under the 2021 ATM program for net proceeds of approximately $ 38.4 million and $ 17.5 million, respectively, after deducting commissions paid to TD Cowen and other financing costs. The Form S-3 registration statement, which registered the 2021 ATM Program, expired on August 15, 2024. As a result, no further shares of common stock may be sold under the 2021 ATM Program. Common Stock The holders of the Company’s common stock have one vote for each share of common stock. Common stockholders are entitled to dividends when, as, and if declared by the board of directors. The holders have no preemptive or other subscription rights and there are no redemption or sinking fund provisions with respect to such shares. As of December 31, 2024, no dividends had been declared by the board of directors. The Company reserved the following shares of common stock for issuance as follows: December 31, 2024 2023 Stock options issued and outstanding 14,594,720 9,208,970 Stock options reserved for 2020 Incentive Award Plan 2,109,758 1,988,340 Unvested restricted stock units outstanding 770,028 495,579 Common stock reserved for 2021 ATM program — 2,619,471 Common stock reserved for 2024 ATM program 24,250,000 — Common stock reserved for Employee Stock Purchase Plan 1,983,924 1,338,381 Common stock reserved for 2022 Employment Inducement 3,359,230 758,084 Common stock reserved for pre-funded warrants 38,543,577 40,493,510 Common stock reserved for common warrants 8,104,615 8,427,508 Total common stock reserved 93,715,852 65,329,843

Equity Incentive Plan

Equity Incentive Plan	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Equity Incentive Plan	7. Equity Incentive Plan In July 2020, the Company’s board of directors and stockholders adopted and approved the 2020 Incentive Award Plan, or the 2020 Plan, and the Employee Stock Purchase Plan, or the ESPP, which became effective in connection with the IPO. The Company may not grant any additional awards under the 2011 Equity Incentive Plan, or the 2011 Plan. The 2011 Plan will continue to govern outstanding equity awards granted thereunder. 2020 Equity Incentive Plan The number of shares of common stock reserved for issuance under the 2020 Plan automatically increase on the first day of January, in an amount equal to 4 % of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company’s board of directors. Awards granted under the 2020 Plan expire no later than ten years from the date of grant. For the Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs, the option price shall not be less than 100 % of the estimated fair value on the date of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms. As of December 31, 2024 and 2023, there were 2,109,758 and 1,988,340 shares available for issuance under the 2020 Plan, respectively. 2022 Employment Inducement Award Plan In July 2022, the Company’s board of directors adopted the Annexon, Inc. 2022 Employment Inducement Award Plan, or the Inducement Plan, and together with the 2011 Plan and the 2020 Plan, the Plans. The Inducement Plan was adopted by the Company’s board of directors without stockholder approval pursuant to Nasdaq Marketplace Rule 5635(c)(4), or Rule 5635(c)(4). In accordance with Rule 5635(c)(4), awards made under the Inducement Plan may only be granted to newly hired employees as an inducement material to the employees entering into employment with the Company. Awards granted under the Inducement Plan expire no later than ten years from the date of grant. An aggregate of 7,850,000 shares of common stock were reserved for issuance under the Inducement Plan. As of December 31, 2024 and 2023, there were 3,359,230 and 758,084 shares available for issuance under the Inducement Plan, respectively. Stock options The following table presents stock option activity under the Plans for the period: Number of Weighted- Weighted- Aggregate Balances as of December 31, 2023 9,208,970 $ 10.31 7.53 $ 2,930 Stock options granted 6,749,824 $ 5.73 Stock options exercised ( 382,122 ) $ 3.22 Stock options forfeited ( 981,952 ) $ 11.55 Balances as of December 31, 2024 14,594,720 $ 8.29 7.94 $ 4,059 Vested and Exercisable as of December 31, 2024 6,813,637 $ 11.06 6.58 $ 2,194 The total intrinsic value of options exercised during the years ended December 31, 2024 and 2023 was $ 1.2 million and $ 0.3 million, respectively. The intrinsic value is the difference between the fair value of the Company’s common stock at the time of exercise and the exercise price of the stock option. The weighted-average grant date fair value of options granted to employees during the years ended December 31, 2024 and 2023 was $ 4.56 and $ 3.72 per share, respectively. As of December 31, 2024, the total unrecognized stock-based compensation cost related to outstanding unvested stock options was $ 33.1 million, which the Company expects to recognize over an estimated weighted-average period of 3.0 years. Restricted Stock Units RSUs are share awards that entitle the holder to receive freely tradeable shares of the Company’s common stock upon vesting. The RSUs cannot be transferred and the awards are subject to forfeiture if the holder’s employment terminates prior to the release of the vesting restrictions. The RSUs generally vest over a three-year period in equal amounts on an annual basis, provided the employee remains continuously employed with the Company. The fair value of the RSUs is equal to the closing price of the Company’s common stock on the grant date. A summary of RSU activity under the equity incentive plan and related information is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Unvested as of December 31, 2023 495,579 $ 5.69 Granted 602,600 5.13 Vested ( 197,177 ) 5.85 Cancelled ( 130,974 ) 5.29 Unvested as of December 31, 2024 770,028 $ 5.28 As of December 31, 2024, unrecognized stock-based compensation expense related to outstanding unvested RSUs was $ 2.5 million, which is expected to be recognized over a weighted-average period of 1.9 years. Employee Stock Purchase Plan The ESPP enables eligible employees to purchase shares of the Company’s common stock at the end of each offering period at a price equal to 85 % of the fair market value of the shares on the first business day or the last business day of the offering period, whichever is lower. Eligible employees generally included all employees. Share purchases are funded through payroll deductions of at least 1 %, and up to 15 % of an employee’s eligible compensation for each payroll period. The number of shares reserved for issuance under the ESPP increase automatically on the first day of each fiscal year, by a number equal to, 1 % of the shares of common stock outstanding on the last day of the immediately preceding fiscal year, or such number of shares determined by the Company’s board of directors. As of December 31, 2024, 1,983,924 shares were available for future purchase. The ESPP generally provides for six-month consecutive offering periods beginning on May 15 th and November 15 th of each year. The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. As such, stock-based compensation expense has been recorded for the years ended December 31, 2024 and 2023. The stock-based compensation expense related to the ESPP for the years ended December 31, 2024 and 2023 was $ 0.2 million and $ 0.3 million, respectively. Stock-Based Compensation Expense The total stock-based compensation expense recognized was as follows (in thousands): Year Ended 2024 2023 Research and development $ 9,670 $ 8,878 General and administrative 9,763 9,305 Total stock-based compensation expense $ 19,433 $ 18,183 To determine the value of stock option awards for stock-based compensation purposes, the Company uses the Black-Scholes option pricing model and the assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment. Fair Value of Common Stock —The fair value of each share of underlying common stock is based on the closing price of the Company’s common stock as reported on the date of grant on the Nasdaq Global Select Market. Expected Term —The expected term represents the period that the stock-based awards are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). The Company continues using the simplified method as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited period of time its equity shares have been publicly traded. Expected Volatility —Beginning in 2024, the expected volatility was estimated based on a weighted volatility using both the Company’s trading history for its common stock and the average volatility for comparable publicly traded life sciences companies over a period equal to the expected term of the stock option grants. Prior to 2024, the expected volatility was estimated based on the average volatility for comparable publicly traded life sciences companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on the similar size, stage in life cycle or area of specialty. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of the option. Dividend Yield —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. The fair value of each stock option issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Year Ended 2024 2023 Expected term (in years) 5.50 - 6.08 5.50 - 6.08 Expected volatility 95.90 % - 99.80 % 81.20 % - 82.40 % Risk-free interest rate 3.48 % - 4.65 % 3.47 % - 4.85 % Dividend yield — —

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes For financial reporting purposes, loss before provision for income taxes, includes the following components (in thousands): Year Ended December 31, 2024 2023 Domestic $ ( 138,193 ) $ ( 134,233 ) Foreign ( 7 ) ( 4 ) Loss before income taxes $ ( 138,200 ) $ ( 134,237 ) For each of the years ended December 31, 2024 and 2023, the Company incurred insignificant amounts for an income tax provision. The U.S. federal and California deferred tax assets generated from the Company’s net operating losses have been fully reserved, as the Company believes it is not more likely than not that the benefit will be realized. Reconciliation of income tax computed at federal statutory rates to the reported provision for income taxes was as follows (in thousands): Year Ended December 31, 2024 2023 Tax provision at U.S. statutory rate $ ( 29,022 ) $ ( 28,190 ) Stock-based compensation 1,548 1,343 Research and development tax credits ( 9,526 ) ( 3,883 ) Change in valuation allowance 35,184 29,066 Section 162(m) compensation 1,773 1,594 Other 43 70 Provision for income taxes $ — $ — Deferred Tax Assets and Liabilities The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2024 2023 Deferred Tax Assets: Net operating loss carryforwards $ 94,198 $ 70,996 Research and development credits 29,095 16,070 Other intangibles 5 3 Accruals and reserves 1,116 1,074 Stock-based compensation 5,599 5,185 Capitalized research and development 49,837 36,568 Lease liabilities 6,087 6,610 Total gross deferred tax assets 185,937 136,506 Less: valuation allowance ( 180,958 ) ( 130,939 ) Total deferred tax assets, net $ 4,979 $ 5,567 Deferred Tax Liabilities: Fixed assets $ ( 1,469 ) $ ( 1,771 ) Right-of-use assets ( 3,510 ) ( 3,796 ) Total gross deferred tax liabilities ( 4,979 ) ( 5,567 ) Net deferred tax assets $ — $ — During 2024, the Company completed a research credit study for the years ended December 31, 2020 through 2023. This resulted in true ups to the credit carryovers, which also impacted the Section 174 capitalized research expenses and net operating losses deferred tax assets disclosed. As of December 31, 2024, the Company had $ 367.7 million of federal and $ 223.8 million of state net operating loss, or NOL, carryforwards available to offset future taxable income. Under the Tax Cuts and Jobs Act of 2017, or the Tax Act, federal NOLs generated after December 31, 2017 will be carried forward indefinitely with the yearly NOL utilization limited to 80 % of taxable income. The Company has $ 324.7 million of such federal NOLs that do not expire. If not utilized, the federal carryforward losses generated prior to 2018 and the state carryforward losses will expire in various amounts beginning in 2031 . As of December 31, 2024, the Company had approximately $ 33.2 million of federal and $ 9.3 million of state credit carryforwards available to offset future taxable income. If not utilized, these credit carryforwards will expire in various amounts for federal purposes beginning in 2031 . The state credits do not expire. In assessing the realization of deferred tax assets, management considers whether it is more likely than not some portion or all of the deferred tax assets will not be realized. Management believes that, based on available evidence, both positive and negative, it is more likely than not that the deferred tax assets will not be utilized; therefore, a full valuation allowance has been recorded. The Company’s valuation allowance increased by $ 50.0 million and $ 30.2 million for the years ended December 31, 2024 and 2023, respectively. The changes in the 2024 valuation allowance were primarily due to the addition of capitalized research and development costs, current year loss carryforwards and research and development credits. The changes in the 2023 valuation allowance were primarily due to the addition of capitalized research and development costs, current year loss carryforwards and research and development credits. Utilization of the net operating loss carryforwards and credits may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended and similar state provisions. The annual limitations may result in the expiration of net operating losses and credits before utilization. The Company performed a Section 382 analysis through December 31, 2024. Federal net operating loss carryforwards of $ 367.6 million and state and local net operating loss carryforwards of $ 189.2 million are not expected to expire unutilized as a result of ownership changes identified through December 31, 2024. The Company has identified $ 0.1 million and $ 34.7 million of federal and state net operating losses, respectively, that will expire unused due to ownership changes, and federal credits of $ 4.3 million that will not be able to be utilized due to ownership change limitation; these amounts have been excluded from the deferred tax assets table above. Further ownership changes subsequent to December 31, 2024 may be identified which could result in limitations to the amount of net operating losses and credits which may be utilized prior to expiration. Uncertain Tax Benefits The Company has the following activity relating to the gross amount of unrecognized tax benefits (in thousands): Year Ended December 31, 2024 2023 Beginning balance $ 3,970 $ 2,726 Additions based on tax positions related to prior year 3,388 189 Reductions based on tax positions related to prior year ( 1,726 ) — Additions based on tax positions related to current year 2,787 1,055 Ending balance $ 8,419 $ 3,970 None of these uncertain tax positions will impact the Company’s effective tax rate if assessed. The Company’s policy is to classify interest and penalties associated with unrecognized tax benefits as income tax expense. The Company had no interest or penalty accruals associated with uncertain tax benefits in its consolidated balance sheet and consolidated statement of operations for the years ended December 31, 2024 and 2023. The Company files income tax returns in the United States, various states, and Australia. The Company is not currently under examination by any major tax jurisdictions nor has it been in the past. The tax years 2011 through 2024 remain effectively open for examination by the Internal Revenue Service and most state tax authorities because of net operating losses and credit carryovers. Although it is reasonably possible that certain unrecognized tax benefits may increase or decrease within the next twelve months due to tax examination changes, settlement activities, expirations of statute of limitations, or the impact on recognition and measurement considerations related to the results of published tax cases or other similar activities, the Company does not anticipate any significant changes to unrecognized tax benefits over the next 12 months.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share The Company calculates basic net loss per share by dividing net loss by the weighted-average number of shares of common stock outstanding. The weighted-average number of shares of common stock used in the basic and diluted net loss per share calculation include pre-funded warrants to purchase up to 38,543,577 and 40,492,923 shares of common stock for the years ended December 31, 2024 and 2023, respectively, as the pre-funded warrants are exercisable at any time for nominal cash consideration. The Company has generated a net loss in all periods presented, so the basic and diluted net loss per share are the same, as the inclusion of the potentially dilutive securities would be anti-dilutive. The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Year Ended 2024 2023 Stock options to purchase common stock 14,594,720 9,208,970 Shares subject to Employee Stock Purchase Plan 15,922 17,200 Unvested restricted stock units 770,028 495,579 Common warrants 8,104,615 8,427,508 Total 23,485,285 18,149,257

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Segment Reporting	10. Segment Reporting The Company has one reportable segment, which is related to the research and development of its product candidates focused on complement-mediated diseases of the body, brain and eye for which there is significant unmet medical need. The accounting policies of the one reportable segment are the same as those described in the summary of significant accounting policies. See Note 2— Basis of Presentation and Significant Accounting Policies . The segment is managed on a consolidated basis and the CODM uses total operating expenses and consolidated net loss to assess performance, forecast future financial results and allocate resources. In assessing the Company's financial performance and making strategic decisions, the CODM regularly reviews operating expenses by function. This includes a review of budget versus actual expenses and direct program spend, which includes clinical costs, consultant fees, manufacturing expenses, and other direct external costs. The following table presents the operations for the reportable segment during the years ended December 31, 2024 and 2023 (in thousands): Year Ended 2024 2023 Research and development - program expenses (1) $ 79,548 $ 76,008 Research and development - personnel 24,291 23,893 General and administrative - personnel 6,578 6,896 Other general and administrative expenses (2) 22,073 16,595 Depreciation expense 2,150 2,148 Stock-based compensation 19,433 18,183 Total operating expense 154,073 143,723 Loss from operations ( 154,073 ) ( 143,723 ) Interest and other income, net 15,873 9,486 Consolidated segment net loss $ ( 138,200 ) $ ( 134,237 ) __________________ (1) Research and development - program expenses include other non-program specific expenses and other research expenses. (2) Other general and administrative expenses include consulting and professional services fees for legal, accounting, tax, and facilities costs.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. Management evaluates its estimates, including but not limited to the fair value of investments, operating lease right-of-use assets and liabilities, valuation of deferred tax assets and uncertain tax positions (including valuation allowance), clinical trial accruals and stock-based compensation. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the operations of Annexon, Inc. and its wholly owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation.
Segments	Segments The Company’s chief operating decision maker ("CODM") is its Chief Executive Officer. The CODM reviews financial information on an aggregate basis for the purposes of evaluating financial performance and allocating the Company’s resources. Accordingly, the Company has determined that it operates in one segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid instruments with an original maturity of three months or less at time of purchase to be cash equivalents. Cash equivalents, which includes amounts invested in money market funds and short-term government bonds, are stated at fair value. Restricted cash as of December 31, 2024 relates to the letters of credit established for the Company’s office lease. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows (in thousands): December 31, 2024 2023 Cash $ 2,651 $ 8,488 Cash equivalents 46,847 216,622 Cash and cash equivalents 49,498 225,110 Restricted cash 1,032 1,032 Cash, cash equivalents and restricted cash $ 50,530 $ 226,142
Short-Term Investments	Short-Term Investments Short-term investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. The Company determines the appropriate classification of its investments in debt securities at the time of purchase. Available-for-sale securities with original maturities beyond three months at the date of purchase are classified as current based on their availability for use in current operations. The Company evaluates, on a quarterly basis, its available-for-sale debt securities for potential impairment. For available-for-sale debt securities in an unrealized loss position, the Company assesses whether such declines are due to credit loss based on factors such as changes to the rating of the security by a ratings agency, market conditions and supportable forecasts of economic and market conditions, among others. If credit loss exists, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale debt security before recovery of its amortized cost basis. If either condition is met, the security’s amortized cost basis is written down to fair value and is recognized through interest and other income (expense), net. If neither condition is met, declines as a result of credit losses, if any, are recognized as an allowance for credit loss, limited to the amount of unrealized loss, through interest and other income (expense), net. Any portion of the unrealized loss that is not a result of a credit loss, is recognized in other comprehensive income (loss). Realized gains and losses, if any, on available-for-sale debt securities are included in interest and other income (expense), net. The cost of investments sold is based on the specific-identification method. Interest on available-for-sale debt securities is included in interest and other income (expense), net.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. The useful lives of the property and equipment are as follows: Computer equipment 3 years Lab equipment and furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. When indications of impairment are present and the estimated undiscounted future cash flows from the use of these assets is less than the assets’ carrying value, the related assets will be written down to fair value. There were no impairments of the Company’s long-lived assets for the periods presented.
Leases	Leases The Company determines if an arrangement is a lease at inception. The Company includes operating leases in operating lease right of use, or ROU, assets, current and noncurrent operating lease liabilities in the Company’s consolidated balance sheets. The ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The Company measures the ROU assets based on the associated lease liabilities adjusted for any lease incentives such as tenant improvement allowances. As most of the leases do not provide an implicit rate, the Company generally uses its incremental borrowing rate based on the estimated rate of interest for collateralized borrowing over a similar term of the lease payments at the commencement date. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise the option. Lease expense for lease payments is recognized on a straight-line basis, net of sublease income, over the lease term. As a practical expedient, the Company elected, for all facility leases, not to separate non-lease components from lease components and instead to account for each separate lease component and its associated non-lease components as a single lease component. The Company elected to exclude from its balance sheets recognition of leases having a term of 12 months or less (short-term leases).
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Valuation allowances are established when necessary to reduce deferred taxes to the amounts expected to be realized. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merit, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Commitments and Contingencies	Commitments and Contingencies Liabilities for loss contingencies arising from claims, assessments, litigation, fines, and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred.
Warrants	Warrants Warrants are accounted for as either derivative liabilities or as equity instruments depending on the specific terms of the agreement. The Company’s pre-funded and common warrants are equity-classified instruments that were recorded in additional paid-in capital at issuance and are not subject to remeasurement. The Company periodically evaluates changes in facts and circumstances that could impact the classification of warrants.
Research and Development Expense	Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials and commercial materials to support future biologics license applications ("BLA") to the FDA, and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. The Company also estimates manufacturing costs based on services performed pursuant to contracts with contract manufacturing organizations that develop and manufacture product on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust the accrual accordingly to reflect the best information available at the time of the financial statement issuance. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees and non-employee directors and consultants using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options and restricted stock units, or RSUs. The fair value method requires the Company to estimate the fair value of stock options to employees and non-employees on the date of grant using the Black-Scholes option pricing model. The fair value of RSU awards is based on the fair value of the underlying common stock as of the grant date. Stock-based compensation costs are based on the fair value of the underlying RSUs and options and recognized as expense on a straight-line basis over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures as they occur.
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share because the effects of potentially dilutive securities are antidilutive.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. The Company’s cash and cash equivalents and short-term investments are held by high credit quality financial institutions in the United States. At times, such deposits may be in excess of the Federal Depository Insurance Corporation insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions.
Recently Adopted/Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (ASU) 2023-07, Segment Reporting: Improvements to Reportable Segment Disclosures , which requires disclosure of incremental segment information on an interim and annual basis. This ASU is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal periods beginning after December 15, 2024, and requires retrospective application to all prior periods presented in the financial statements. The Company adopted annual and interim requirements under ASU 2023-07 on January 1, 2024 and 2025, respectively. The adoption of ASU 2023-07 did no t have a material impact on the Company's consolidated financial statements. See Note 10 — Segment Reporting. Recently Issued Accounting Pronouncements In December 2023, the FASB issued ASU 2023-09, Income Taxes: Improvements to Income Tax Disclosures , which requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures : Disaggregation of Income Statement Expenses , which requires public entities to disclose additional information about specific expense categories in the notes to the financial statements on an interim and annual basis. This guidance is effective for annual reporting periods beginning after December 15, 2026, and interim periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows (in thousands): December 31, 2024 2023 Cash $ 2,651 $ 8,488 Cash equivalents 46,847 216,622 Cash and cash equivalents 49,498 225,110 Restricted cash 1,032 1,032 Cash, cash equivalents and restricted cash $ 50,530 $ 226,142
Schedule of Useful Lives of Property and Equipment	The useful lives of the property and equipment are as follows: Computer equipment 3 years Lab equipment and furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2024 Valuation Amortized Gross Gross Aggregate Assets: Cash equivalents: Money market funds Level 1 $ 31,680 $ — $ — $ 31,680 Government bonds Level 2 15,167 — — 15,167 Total cash equivalents 46,847 — — 46,847 Short-term investments: Government bonds Level 2 262,424 98 ( 3 ) 262,519 Total short-term investments 262,424 98 ( 3 ) 262,519 $ 309,271 $ 98 $ ( 3 ) $ 309,366 December 31, 2023 Valuation Amortized Gross Gross Aggregate Assets: Cash equivalents: Money market funds Level 1 $ 143,933 $ — $ — $ 143,933 Government bonds Level 2 72,689 — — 72,689 Total cash equivalents 216,622 — — 216,622 Short-term investments: Government bonds Level 2 34,596 10 — 34,606 Total short-term investments 34,596 10 — 34,606 $ 251,218 $ 10 $ — $ 251,228

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2024
Disclosure Of Balance Sheet Components [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2024 2023 Prepaid research and development costs $ 2,640 $ 2,617 Prepaid insurance 700 704 Prepaid and other current assets 1,104 823 Total prepaid expenses and other current assets $ 4,444 $ 4,144
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): December 31, 2024 2023 Leasehold improvements $ 17,254 $ 17,245 Laboratory equipment 1,838 1,832 Furniture and fixtures 692 692 Computer equipment and software 33 33 Total property and equipment, gross 19,817 19,802 Less: accumulated depreciation ( 7,179 ) ( 5,029 ) Total property and equipment, net $ 12,638 $ 14,773
Summary of Accrued and Other Current Liabilities	Accrued and other current liabilities consisted of the following (in thousands): December 31, 2024 2023 Accrued research and development expenses $ 10,992 $ 4,027 Accrued compensation 5,833 5,607 Accrued professional services 602 501 Other accrued and current liabilities 141 141 Total accrued and other current liabilities $ 17,568 $ 10,276

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Lease Payments and Related Lease Liabilities	Future minimum lease payments and related lease liabilities as of December 31, 2024 were as follows: (in thousands) 2025 $ 5,065 2026 5,242 2027 5,425 2028 5,615 2029 and thereafter 16,985 Total undiscounted lease payments 38,332 Less: Imputed interest ( 9,360 ) Total $ 28,972

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	12 Months Ended
	Dec. 31, 2024
Stockholders' Equity Note [Abstract]
Summary of Warrants Activity	The following summarizes warrant activity during the years ended December 31, 2024 and 2023: Number of Common Warrants Number of Pre-funded Warrants Weighted-Average Exercise Price Balances as of December 31, 2022 8,427,508 24,696,206 Issued — 18,379,861 $ 0.001 Exercised — ( 2,583,144 ) $ 0.001 Balances as of December 31, 2023 8,427,508 40,492,923 Issued — 7,000,000 $ 0.001 Exercised ( 322,893 ) ( 8,949,346 ) $ 0.216 Balances as of December 31, 2024 8,104,615 38,543,577
Schedule of Common Stock Reserved for Future Issuance	The Company reserved the following shares of common stock for issuance as follows: December 31, 2024 2023 Stock options issued and outstanding 14,594,720 9,208,970 Stock options reserved for 2020 Incentive Award Plan 2,109,758 1,988,340 Unvested restricted stock units outstanding 770,028 495,579 Common stock reserved for 2021 ATM program — 2,619,471 Common stock reserved for 2024 ATM program 24,250,000 — Common stock reserved for Employee Stock Purchase Plan 1,983,924 1,338,381 Common stock reserved for 2022 Employment Inducement 3,359,230 758,084 Common stock reserved for pre-funded warrants 38,543,577 40,493,510 Common stock reserved for common warrants 8,104,615 8,427,508 Total common stock reserved 93,715,852 65,329,843

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Summary of Stock Option Activity	The following table presents stock option activity under the Plans for the period: Number of Weighted- Weighted- Aggregate Balances as of December 31, 2023 9,208,970 $ 10.31 7.53 $ 2,930 Stock options granted 6,749,824 $ 5.73 Stock options exercised ( 382,122 ) $ 3.22 Stock options forfeited ( 981,952 ) $ 11.55 Balances as of December 31, 2024 14,594,720 $ 8.29 7.94 $ 4,059 Vested and Exercisable as of December 31, 2024 6,813,637 $ 11.06 6.58 $ 2,194
Summary of RSU Activity under Equity Incentive Plan	A summary of RSU activity under the equity incentive plan and related information is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Unvested as of December 31, 2023 495,579 $ 5.69 Granted 602,600 5.13 Vested ( 197,177 ) 5.85 Cancelled ( 130,974 ) 5.29 Unvested as of December 31, 2024 770,028 $ 5.28
Summary of Stock-Based Compensation Expense	The total stock-based compensation expense recognized was as follows (in thousands): Year Ended 2024 2023 Research and development $ 9,670 $ 8,878 General and administrative 9,763 9,305 Total stock-based compensation expense $ 19,433 $ 18,183
Summary of Fair Value of Each Stock Option Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model	The fair value of each stock option issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Year Ended 2024 2023 Expected term (in years) 5.50 - 6.08 5.50 - 6.08 Expected volatility 95.90 % - 99.80 % 81.20 % - 82.40 % Risk-free interest rate 3.48 % - 4.65 % 3.47 % - 4.85 % Dividend yield — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Components of Loss Before Income Taxes	For financial reporting purposes, loss before provision for income taxes, includes the following components (in thousands): Year Ended December 31, 2024 2023 Domestic $ ( 138,193 ) $ ( 134,233 ) Foreign ( 7 ) ( 4 ) Loss before income taxes $ ( 138,200 ) $ ( 134,237 )
Reconciliation of Income Tax Computed at Federal Statutory Rates to Provision for Income Taxes	Reconciliation of income tax computed at federal statutory rates to the reported provision for income taxes was as follows (in thousands): Year Ended December 31, 2024 2023 Tax provision at U.S. statutory rate $ ( 29,022 ) $ ( 28,190 ) Stock-based compensation 1,548 1,343 Research and development tax credits ( 9,526 ) ( 3,883 ) Change in valuation allowance 35,184 29,066 Section 162(m) compensation 1,773 1,594 Other 43 70 Provision for income taxes $ — $ —
Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2024 2023 Deferred Tax Assets: Net operating loss carryforwards $ 94,198 $ 70,996 Research and development credits 29,095 16,070 Other intangibles 5 3 Accruals and reserves 1,116 1,074 Stock-based compensation 5,599 5,185 Capitalized research and development 49,837 36,568 Lease liabilities 6,087 6,610 Total gross deferred tax assets 185,937 136,506 Less: valuation allowance ( 180,958 ) ( 130,939 ) Total deferred tax assets, net $ 4,979 $ 5,567 Deferred Tax Liabilities: Fixed assets $ ( 1,469 ) $ ( 1,771 ) Right-of-use assets ( 3,510 ) ( 3,796 ) Total gross deferred tax liabilities ( 4,979 ) ( 5,567 ) Net deferred tax assets $ — $ —
Unrecognized Tax Benefits	The Company has the following activity relating to the gross amount of unrecognized tax benefits (in thousands): Year Ended December 31, 2024 2023 Beginning balance $ 3,970 $ 2,726 Additions based on tax positions related to prior year 3,388 189 Reductions based on tax positions related to prior year ( 1,726 ) — Additions based on tax positions related to current year 2,787 1,055 Ending balance $ 8,419 $ 3,970

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Year Ended 2024 2023 Stock options to purchase common stock 14,594,720 9,208,970 Shares subject to Employee Stock Purchase Plan 15,922 17,200 Unvested restricted stock units 770,028 495,579 Common warrants 8,104,615 8,427,508 Total 23,485,285 18,149,257

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Schedule of Operations for Reportable Segment	The following table presents the operations for the reportable segment during the years ended December 31, 2024 and 2023 (in thousands): Year Ended 2024 2023 Research and development - program expenses (1) $ 79,548 $ 76,008 Research and development - personnel 24,291 23,893 General and administrative - personnel 6,578 6,896 Other general and administrative expenses (2) 22,073 16,595 Depreciation expense 2,150 2,148 Stock-based compensation 19,433 18,183 Total operating expense 154,073 143,723 Loss from operations ( 154,073 ) ( 143,723 ) Interest and other income, net 15,873 9,486 Consolidated segment net loss $ ( 138,200 ) $ ( 134,237 ) __________________ (1) Research and development - program expenses include other non-program specific expenses and other research expenses. (2) Other general and administrative expenses include consulting and professional services fees for legal, accounting, tax, and facilities costs.

Organization - Additional Infor

Organization - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Accumulated deficit	$ 710,699	$ 572,499
Cash and cash equivalents and short-term investments	$ 312,000

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2024 USD ($) Segment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Number of operating segment | Segment	1
Impairments of long-lived assets | $	$ 0
ASU 2023-07 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Change in accounting principle, ASU adopted	true
Change in accounting principle, ASU, adoption date	Jan. 01, 2024
Change in accounting principle, ASU, Immaterial effect	true

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash	$ 2,651	$ 8,488
Cash equivalents	46,847	216,622
Cash and cash equivalents	49,498	225,110
Restricted cash	1,032	1,032
Cash, cash equivalents and restricted cash	$ 50,530	$ 226,142

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Schedule of Useful Lives of Property and Equipment (Detail)	Dec. 31, 2024
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 309,271	$ 251,218
Gross Unrealized Holding Gains	98	10
Gross Unrealized Holding Losses	(3)
Aggregate Fair Value	309,366	251,228
Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	46,847	216,622
Aggregate Fair Value	46,847	216,622
Level 1 [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	31,680	143,933
Aggregate Fair Value	31,680	143,933
Level 2 [Member] | Cash and Cash Equivalents [Member] | Government Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	15,167	72,689
Aggregate Fair Value	15,167	72,689
Level 2 [Member] | Short-Term Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	262,424	34,596
Gross Unrealized Holding Gains	98	10
Gross Unrealized Holding Losses	(3)
Aggregate Fair Value	262,519	34,606
Level 2 [Member] | Short-Term Investments [Member] | Government Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	262,424	34,596
Gross Unrealized Holding Gains	98	10
Gross Unrealized Holding Losses	(3)
Aggregate Fair Value	$ 262,519	$ 34,606

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2024 USD ($)
Fair Value Disclosures [Abstract]
Investment maturity period	2 years
Credit losses	$ 0
Allowance for doubtful accounts	0
Unrealized loss position for more than 12 months	$ 0
Investment expected maturity period	12 months

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid research and development costs	$ 2,640	$ 2,617
Prepaid insurance	700	704
Prepaid and other current assets	1,104	823
Total prepaid expenses and other current assets	$ 4,444	$ 4,144

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 19,817	$ 19,802
Less: accumulated depreciation	(7,179)	(5,029)
Total property and equipment, net	12,638	14,773
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	17,254	17,245
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	1,838	1,832
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	692	692
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 33	$ 33

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Prepaid Expense and Other Assets, Current [Abstract]
Depreciation expense	$ 2.2	$ 2.1

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Accrued and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Accrued Liabilities, Current [Abstract]
Accrued research and development expenses	$ 10,992	$ 4,027
Accrued compensation	5,833	5,607
Accrued professional services	602	501
Other accrued and current liabilities	141	141
Total accrued and other current liabilities	$ 17,568	$ 10,276

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	12 Months Ended		24 Months Ended
	Nov. 30, 2021	Dec. 31, 2024 USD ($) Claim	Dec. 31, 2023 USD ($)	Nov. 30, 2023 USD ($)
Gain Contingencies [Line Items]
Aggregate sublease payment receivable				$ 3,400,000
Sublease Income		$ 0	$ 2,000,000
Operating lease right-of-use assets		16,705,000	18,009,000
Lease liabilities		$ 28,972,000
Weighted average incremental borrowing rate		8.40%
Operating lease cost		$ 3,800,000	2,300,000
Variable lease payments		2,300,000	$ 1,500,000
Loss contingency accrual		$ 0
Indemnification Agreement [Member]
Gain Contingencies [Line Items]
Loss contingency pending claims | Claim		0
Brisbane, California [Member]
Gain Contingencies [Line Items]
Operating lease, term of contract		10 years
Operating lease, expiration month and year		2031-10
Operating lease, renewal term		10 years
Sublease starting year and month	2021-12
Sublease expiration year and month	2023-11
Operating lease right-of-use assets		$ 16,700,000
Lease liabilities		$ 29,000,000
Weighted average remaining lease term		6 years 9 months 18 days

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments and Related Lease Liabilities (Detail) $ in Thousands	Dec. 31, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2025	$ 5,065
2026	5,242
2027	5,425
2028	5,615
2029 and thereafter	16,985
Total undiscounted lease payments	38,332
Less: Imputed interest	(9,360)
Lease liabilities	$ 28,972

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended									12 Months Ended
	Nov. 30, 2024	Jun. 30, 2024	Apr. 30, 2024	Mar. 31, 2024	Feb. 29, 2024	Dec. 31, 2023	Mar. 31, 2023	Jul. 31, 2022	Aug. 31, 2021	Dec. 31, 2024	Dec. 31, 2023
Class Of Stock [Line Items]
Net proceeds from private placement								$ 122,500
Common stock, par value per share						$ 0.001				$ 0.001	$ 0.001
Common stock, voting rights										The holders of the Company’s common stock have one vote for each share of common stock.
Common stock, dividends declared										$ 0
Common stock						$ 78				$ 109	$ 78
Common stock, shares issued						78,369,099				109,381,556	78,369,099
Net proceeds from sale of common stock										$ 44,371	$ 17,995
Pre-funded Warrants [Member]
Class Of Stock [Line Items]
Purchase of shares		7,000,000				18,379,861					18,379,861
Offering price per share		$ 6.249				$ 2.879		$ 3.87025
Pre-funded Warrants [Member] | Maximum [Member]
Class Of Stock [Line Items]
Purchase of shares								24,696,206
Purchase price per share		$ 0.001				$ 0.001		$ 0.001			$ 0.001
Warrants or Common Warrants [Member]
Class Of Stock [Line Items]
Offering price per share								3.87125
Purchase price per share								$ 5.806875
Warrant expiration date								Jun. 30, 2025
Warrants or Common Warrants [Member] | Maximum [Member]
Class Of Stock [Line Items]
Purchase of shares								8,427,508
Common Stock [Member]
Class Of Stock [Line Items]
Sale of shares										8,326,067
Common stock shares issued for exercise of warrants	2,739,096	19,901	965,427		5,243,400		2,582,557
Private Placement [Member]
Class Of Stock [Line Items]
Sale of shares								9,013,834
Underwriting agreement [Member]
Class Of Stock [Line Items]
Sale of shares		13,001,120				25,035,000
Common stock, par value per share		$ 0.001				$ 0.001					0.001
Exchange value						$ 1,000
Shares issued price per share		$ 6.25				$ 2.88					$ 2.88
Net proceeds from sale of common stock		$ 116,800				$ 117,000
Underwriting agreement [Member] | Director [Member]
Class Of Stock [Line Items]
Sale of shares						350,000
Sales Agreement with Cowen and Company LLC [Member] | 2021 ATM Program [Member]
Class Of Stock [Line Items]
Common stock									$ 100,000
Percentage of gross proceeds of common stock to be paid									3%
Common stock, shares issued						2,646,458				7,576,067	2,646,458
Net proceeds from sale of common stock										$ 38,400	$ 17,500
Sales Agreement with Cowen and Company LLC [Member] | 2024 ATM Program [Member]
Class Of Stock [Line Items]
Common stock				$ 100,000
Remains available for offer and sales of shares of common stock										$ 95,400
Sales Agreement with Cowen and Company LLC [Member] | 2024 ATM Program [Member] | Maximum [Member]
Class Of Stock [Line Items]
Percentage of gross proceeds of common stock to be paid				3%
Sales Agreement with Cowen and Company LLC [Member] | 2024 ATM Program [Member] | Common Stock [Member]
Class Of Stock [Line Items]
Sale of shares										750,000
Net proceeds from sale of common stock										$ 4,500

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Warrants Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Number of Common Warrants [Member]
Class of Warrant or Right [Line Items]
Beginning Balance	8,427,508	8,427,508
Exercised	(322,893)
Ending Balance	8,104,615	8,427,508
Number of Pre-funded Warrants [Member]
Class of Warrant or Right [Line Items]
Beginning Balance	40,492,923	24,696,206
Issued	7,000,000	18,379,861
Exercised	(8,949,346)	(2,583,144)
Ending Balance	38,543,577	40,492,923
Common Warrant and Pre-funded Warrants [Member]
Class of Warrant or Right [Line Items]
Weighted-Average Exercise Price, Issued	$ 0.001	$ 0.001
Weighted-Average Exercise Price, Exercised	$ 0.216	$ 0.001

Stockholder's Equity - Schedule

Stockholder's Equity - Schedule of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2024	Dec. 31, 2023
Class Of Stock [Line Items]
Common stock reserved	14,594,720	9,208,970
Common stock reserved	2,109,758	1,988,340
Common stock reserved	93,715,852	65,329,843
Employee Stock Option
Class Of Stock [Line Items]
Common stock reserved	14,594,720	9,208,970
Stock Options Reserved for 2020 Incentive Award Plan [Member]
Class Of Stock [Line Items]
Common stock reserved	2,109,758	1,988,340
Unvested Restricted Stock Units Outstanding [Member]
Class Of Stock [Line Items]
Common stock reserved	770,028	495,579
Common Stock Reserved for Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock reserved	1,983,924	1,338,381
2022 Employment Inducement Award Plan [Member]
Class Of Stock [Line Items]
Common stock reserved	3,359,230	758,084
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Common stock reserved	38,543,577	40,493,510
Common Warrants [Member]
Class Of Stock [Line Items]
Common stock reserved	8,104,615	8,427,508
2021 ATM Program [Member]
Class Of Stock [Line Items]
Common stock reserved		2,619,471
2024 ATM Program [Member]
Class Of Stock [Line Items]
Common stock reserved	24,250,000

Equity Incentive Plan - Additio

Equity Incentive Plan - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Jul. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of number of shares of capital stock outstanding on last day of preceding year	4%
Stock option grants description	Awards granted under the 2020 Plan expire no later than ten years from the date of grant. For the Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs, the option price shall not be less than 100% of the estimated fair value on the date of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms.
Option expiry period	10 years
Vesting Period	4 years
Options available for future grant	2,109,758	1,988,340
Intrinsic value of options exercised	$ 1,200	$ 300
Weighted- average exercise price per share, Stock options granted	$ 5.73
Unrecognized stock-based compensation cost expected period for recognition	3 years
Common stock for future issuance	93,715,852	65,329,843
Total stock-based compensation expense	$ 19,433	$ 18,183
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted- average exercise price per share, Stock options granted	$ 4.56	$ 3.72
2022 Employment Inducement Award Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options available for future grant	3,359,230	758,084	7,850,000
Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of Common stock at end of each offering period at price equal to percentage of fair market value of shares	100%
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 33,100
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 2,500
Unrecognized stock-based compensation cost expected period for recognition	1 year 10 months 24 days
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of Common stock at end of each offering period at price equal to percentage of fair market value of shares	85%
Share purchases funded through payroll deductions minimum percentage of employee's eligible compensation	1%
Share purchases funded through payroll deductions maximum percentage of employee's eligible compensation	15%
Common stock for future issuance	1,983,924	1,338,381
Percentage of shares of common stock outstanding on last day of immediately preceding fiscal year	1%
Total stock-based compensation expense	$ 200	$ 300

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Number of shares, Beginning balance	9,208,970
Number of shares, Stock options granted	6,749,824
Number of shares, Stock options exercised	(382,122)
Number of shares, Stock options forfeited	(981,952)
Number of shares, Ending balance	14,594,720	9,208,970
Number of shares, Vested and Exercisable	6,813,637
Weighted- average exercise price per share, Beginning balance	$ 10.31
Weighted- average exercise price per share, Stock options granted	5.73
Weighted- average exercise price per share, Stock options exercised	3.22
Weighted- average exercise price per share, Stock options forfeited	11.55
Weighted- average exercise price per share, Ending balance	8.29	$ 10.31
Weighted- average exercise price per share, Exercisable	$ 11.06
Weighted- average remaining contractual term	7 years 11 months 8 days	7 years 6 months 10 days
Weighted- average remaining contractual term, Exercisable	6 years 6 months 29 days
Aggregate intrinsic value	$ 4,059	$ 2,930
Aggregate intrinsic value, Exercisable	$ 2,194

Equity Incentive Plan - Summa_2

Equity Incentive Plan - Summary of RSU Activity under Equity Incentive Plan (Detail)	12 Months Ended
	Dec. 31, 2024 $ / shares shares
Share-Based Payment Arrangement [Abstract]
Number of Shares, Unvested as of December 31, 2023 | shares	495,579
Number of Shares, Granted | shares	602,600
Number of Shares, Vested | shares	(197,177)
Number of Shares, Cancelled | shares	(130,974)
Number of Shares, Unvested as of December 31, 2024 | shares	770,028
Weighted-Average Grant Date Fair Value Per Share, Granted Unvested as of December 31, 2023 | $ / shares	$ 5.69
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	5.13
Weighted-Average Grant Date Fair Value Per Share, Vested | $ / shares	5.85
Weighted-Average Grant Date Fair Value Per Share, Cancelled | $ / shares	5.29
Weighted-Average Grant Date Fair Value Per Share, Granted Unvested as of December 31, 2024 | $ / shares	$ 5.28

Equity Incentive Plan - Summa_3

Equity Incentive Plan - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 19,433	$ 18,183
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	9,670	8,878
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 9,763	$ 9,305

Equity Incentive Plan - Summa_4

Equity Incentive Plan - Summary of Fair Value of Each Stock Option Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	95.90%	81.20%
Expected volatility, Maximum	99.80%	82.40%
Risk-free interest rate, Minimum	3.48%	3.47%
Risk-free interest rate, Maximum	4.65%	4.85%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days

Income Taxes - Components of Lo

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Domestic	$ (138,193)	$ (134,233)
Foreign	(7)	(4)
Loss before income taxes	$ (138,200)	$ (134,237)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Computed at Federal Statutory Rates to Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Tax provision at U.S. statutory rate	$ (29,022)	$ (28,190)
Stock-based compensation	1,548	1,343
Research and development tax credits	(9,526)	(3,883)
Change in valuation allowance	35,184	29,066
Section 162(m) compensation	1,773	1,594
Other	43	70
Provision for income taxes	$ 0	$ 0

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 94,198	$ 70,996
Research and development credits	29,095	16,070
Other intangibles	5	3
Accruals and reserves	1,116	1,074
Stock-based compensation	5,599	5,185
Capitalized research and development	49,837	36,568
Lease liabilities	6,087	6,610
Total gross deferred tax assets	185,937	136,506
Less: valuation allowance	(180,958)	(130,939)
Total deferred tax assets, net	4,979	5,567
Fixed assets	(1,469)	(1,771)
Right-of-use assets	(3,510)	(3,796)
Total gross deferred tax liabilities	(4,979)	(5,567)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax [Line Items]
Federal net operating loss carryforwards	$ 367,700,000
State net operating loss carryforwards	$ 223,800,000
Percentage of taxable income	80%
State carryforward losses expiration beginning year	2031
Increase in valuation allowance	$ 50,000,000	$ 30,200,000
Uncertain tax position	0
Unrecognized tax benefits, interest or penalty accruals	$ 0
Open tax year examination	2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Federal [Member]
Income Tax [Line Items]
NOLs with annual limitation utilization that do not expire	$ 324,700,000
Tax credit carryforwards	$ 33,200,000
Federal carryforward losses expiration beginning year	2031
NOLs do not expire	$ 367,600,000
NOLs subject to expire	100,000
Federal credits	4,300,000
State [Member]
Income Tax [Line Items]
Tax credit carryforwards	9,300,000
NOLs do not expire	189,200,000
NOLs subject to expire	$ 34,700,000

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Beginning balance	$ 3,970	$ 2,726
Additions based on tax positions related to prior year	3,388	189
Reductions based on tax positions related to prior year	(1,726)	0
Additions based on tax positions related to current year	2,787	1,055
Ending balance	$ 8,419	$ 3,970

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - Pre-funded Warrants [Member] - shares	Dec. 31, 2024	Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022	Jul. 31, 2022
Class of Warrant or Right [Line Items]
Warrants exercised		7,000,000	18,379,861
Warrants outstanding	38,543,577		40,492,923	24,696,206
Maximum [Member]
Class of Warrant or Right [Line Items]
Warrants exercised					24,696,206
Maximum [Member] | Common Stock [Member]
Class of Warrant or Right [Line Items]
Warrants exercised	38,543,577		40,492,923

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	23,485,285	18,149,257
Shares Subject to Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	15,922	17,200
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	14,594,720	9,208,970
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	770,028	495,579
Common Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	8,104,615	8,427,508

Segment Reporting - Additional

Segment Reporting - Additional Information (Details)	12 Months Ended
	Dec. 31, 2024 Segment
Segment Reporting [Abstract]
Number of reportable segment	1
Segment Reporting, Expense Information Used by CODM, Description	The segment is managed on a consolidated basis and the CODM uses total operating expenses and consolidated net loss to assess performance, forecast future financial results and allocate resources. In assessing the Company's financial performance and making strategic decisions, the CODM regularly reviews operating expenses by function. This includes a review of budget versus actual expenses and direct program spend, which includes clinical costs, consultant fees, manufacturing expenses, and other direct external costs.

Segment Reporting - Schedule of

Segment Reporting - Schedule of Operations for Reportable Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Research and development	$ 119,448	$ 113,756
General and administrative	34,625	29,967
Depreciation expense	2,200	2,100
Stock-based compensation	19,433	18,183
Total operating expenses	154,073	143,723
Loss from operations	(154,073)	(143,723)
Interest and other income, net	15,873	9,486
Net loss	(138,200)	(134,237)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Other general and administrative expenses	22,073	16,595
Depreciation expense	2,150	2,148
Stock-based compensation	19,433	18,183
Total operating expenses	154,073	143,723
Loss from operations	(154,073)	(143,723)
Interest and other income, net	15,873	9,486
Operating Segments [Member] | Program Expenses [Member]
Segment Reporting Information [Line Items]
Research and development	79,548	76,008
Operating Segments [Member] | Personnel Expenses [Member]
Segment Reporting Information [Line Items]
Research and development	24,291	23,893
General and administrative	$ 6,578	$ 6,896