Annexon, Inc.

1. Organization

Annexon, Inc., or the Company, is a biopharmaceutical company advancing the next generation platform of targeted immunotherapies aimed at complement-mediated neuroinflammatory diseases that impact nearly 10 million people worldwide. 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 March 31, 2026, had an accumulated deficit of$961.5 million and cash and cash equivalents and short-term investments of$225.0 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 and regulatory 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.

2. Basis of Presentation and Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or GAAP, and applicable rules and regulations of the SEC regarding interim financial reporting.

The condensed consolidated balance sheet as of March 31, 2026, the condensed consolidated statements of operations, comprehensive loss, stockholders’ equity for the three months ended March 31, 2026 and 2025 and the condensed consolidated statements of cash flows for the three months ended March 31, 2026 and 2025 are unaudited. These unaudited condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and cash flows for the interim period presented. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three month periods are also unaudited. The results of operations for the three months ended March 31, 2026 are not necessarily indicative of the results to be expected for the year ending December 31, 2026 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2025 included herein was derived from the audited consolidated financial statements as of that date. These unaudited condensed consolidated financial statements should be read in conjunction with the Company's audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC on March 30, 2026.

Use of Estimates

Thepreparation 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, incremental borrowing rate for 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 condensed 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.

Summary of Significant Accounting Policies

Reference is made to Note 2, Summary of Significant Accounting Policies, in the Company’s 2025 Form 10-K filed on March 30, 2026 for a detailed description of significant accounting policies. There have been no significant changes to the Company’s accounting policies as disclosed in its 2025 Form 10-K.

Recently Issued Accounting Pronouncements

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.

In December 2025, the FASB issued ASU 2025-11, Interim Reporting (Topic 270) Narrow-Scope Improvements. The ASU clarifies and reorganizes interim reporting guidance, including disclosure requirements related to events occurring since the end of the most recent annual reporting period, and improves the presentation and usability of interim financial statement disclosures. The ASU is effective for interim reporting periods within fiscal years beginning after December 15, 2027, with early adoption permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.

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:

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Level 1 Inputs: Unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date.

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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.

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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 measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands):

All of the investments held as of March 31, 2026, had original maturities of less thantwo years. As of March 31, 2026, all of the investments are scheduled to mature within 12 months. During the three months ended March 31, 2026, the Company didnot recognize any credit losses. The Company determined that the decline in fair value of debt securities was not due to credit-related factors, andno allowance for expected credit losses was recorded as of March 31, 2026. There were nominal unrealized losses as of March 31, 2026, andno investments 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 three months ended March 31, 2026 and 2025, the Company recognized no material realized gains or losses on financial instruments.

4. Balance Sheet Components

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 include amounts invested in money market funds and government bonds, are stated at fair value.

Restricted cash as of March 31, 2026 relates to the letters of credit established for the Company’s office leases.

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the unaudited condensed consolidated balance sheets that sum to the total of the same amounts shown in the unaudited condensed consolidated statements of cash flows (in thousands):

Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):

The Company recognized depreciation expense for property and equipment of$0.5 million for each of the three months ended March 31, 2026 and 2025.

Accrued and Other Current Liabilities

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

5. Commitments and Contingencies

Leases

The Company leases its offices and laboratory in Brisbane, California, under aten-year noncancelable lease agreement that ends in October 2031 with aten-year renewable option.

As of March 31, 2026, the operating lease right-of-use assets were$14.8 million and lease liabilities were$25.4 million on the unaudited condensed consolidated balance sheet. The weighted-average remaining lease term is 5.6 years.

The weighted-average incremental borrowing rate used to measure the operating lease liability is 8.4%.

Operating lease costs were$1.0 million for each of the three months ended March 31, 2026 and 2025. Variable lease payments were$0.6 million and $0.7 million for the three months ended March 31, 2026 and 2025, respectively.

Future minimum lease payments and related lease liabilities as of March 31, 2026, were as follows:

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 hasnot paid any claims or been required to defend any action related to its indemnification obligations. As of March 31, 2026, the Company didnot have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

6. Stockholders’ Equity

2025 Financing

In November 2025, the Company raised net proceeds of approximately $80.5 million after deducting underwriting discounts and offering expenses through the sale of 29,423,075 shares of the Company’s common stock at a price of $2.60 per share and pre-funded warrants to purchase an aggregate of 3,750,000 shares of common stock at a price of $2.599 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.

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. In March 2026, the Company issued an aggregate of 4,499,124 shares of common stock upon the cashless exercise of pre-funded warrants to purchase 4,500,000 shares of common stock.

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. In March 2026, the Company issuedan aggregate of 2,027,384 shares of common stock upon the cashless exercise of pre-funded warrants to purchase 2,027,778 shares of common stock.

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 had an exercise price of $5.806875 per share and, except as described in the next paragraph, expired on June 30, 2025. Both the pre-funded and common warrants were 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.

In June 2025, the Company and holders of common warrants exercisable for 6,877,622 shares of the Company’s common stock entered into amendments to the common warrants held by such holders. The amendments extended the term of the common warrants by one year until June 30, 2026, and removed the cashless exercise option. If all such common warrants are exercised in full for cash (without regard to any applicable ownership limitations), the Company would receive aggregate gross proceeds of approximately $39.9 million. The remaining common warrants to purchase 1,226,993 shares of the Company's common stock not subject to these amendments expired unexercised on June 30, 2025.

The Company concluded that the modified common warrants retain equity classification. The excess of fair value of the modified warrants over the fair value of the warrants immediately before the modification of$1.9 million was recognized as a deemed dividend for the year ended December 31, 2025. This modification included a related party transaction involving 613,497 common warrants held by a fund affiliated with a member of our board of directors, which accounted for $0.2 million of the deemed dividend recognized. As the Company had an accumulated deficit as of December 31, 2025, the deemed dividend was recognized in additional paid-in capital with zero net impact on stockholders' equity. There wasno deemed dividend recognized during the three months ended March 31, 2026.

Pre-Funded and Common Warrants

The following summarizes warrant activity during the three months ended March 31, 2026 and 2025:

At the Market (ATM) Program

In March 2026, the Company entered into a sales agreement with TD Securities (USA) LLC, or TD Cowen, as sales agent, pursuant to which the Company may offer and sell, from time to time through TD Cowen, at its option, shares of its common stock having an aggregate offering price of up to $150.0 million, or the 2026 ATM program. The Company agreed to pay TD Cowen a commission of up to 3.0% of the aggregate gross proceeds for the common stock sold through the 2026 ATM program. During the three months ended March 31, 2026, no sales were made under the 2026 ATM program. Subsequent to March 31, 2026 and through the date of issuance of these interim unaudited condensed consolidated financial statements, the Company sold 1,305,463 shares of common stock under the 2026 ATM program for net proceeds of approximately$8.1 million, after deducting commissions paid to TD Cowen.

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. During the three months ended March 31, 2026, the Company sold 6,049,762 shares of its common stock under the 2024 ATM program for net proceeds of approximately$32.7 million, after deducting commissions paid to TD Cowen and other offering costs. Approximately$33.3 million remained available under the 2024 ATM program, which the Company terminated in May 2026.

Common Stock

The Company reserved the following shares of common stock for issuance as follows:

7. Equity Incentive Plans

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 Company’s initial public offering, or 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 Incentive Award Plan

The number of shares of common stock reserved for issuance under the 2020 Plan automatically increases 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 thanten years from the date of grant. For 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 afour-year period but may be granted with different vesting terms. As of March 31, 2026, there were 1,441,747 shares available for issuance under the 2020 Plan.

2022 Employment Inducement Award Plan

In July 2022, the Company’s board of directors adopted the Annexon, Inc. 2022 Employment Inducement Award Plan, as amended, 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 March 31, 2026, there were 3,605,418 shares available for issuance under the Inducement Plan.

Stock Options

The following table presents stock option activity under the Plans for the period:

The total intrinsic value of options exercised was$0.1 million for each of the three months ended March 31, 2026 and 2025. 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 three months ended March 31, 2026 and 2025 was$4.05 and $2.01 per share, respectively.

As of March 31, 2026, the total unrecognized stock-based compensation cost related to outstanding unvested stock options was$37.2 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 Company’s equity incentive plan and related information is as follows:

As of March 31, 2026, unrecognized stock-based compensation expense related to outstanding unvested RSUs was$11.5 million, which is expected to be recognized over a weighted-average period of 2.7 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 include 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

March 31, 2026,4,294,178 shares were available for future purchase. The ESPP generally provides for six-month consecutive offering periods beginning on May 16 and November 16 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 three months ended March 31, 2026.

The stock-based compensation expense related to the ESPP was$47,000 and $40,000 for the three months ended March 31, 2026 and 2025, respectively.

Stock-Based Compensation Expense

The total stock-based compensation expense recognized was as follows (in thousands):

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. 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 2026, the expected volatility assumption is estimated based solely on the historical volatility of the Company’s share trading price for its common stock and is no longer derived from a weighted average that includes comparable publicly traded life sciences companies. Prior to 2026, 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. The comparable companies were chosen based on 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:

8. 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, excluding restricted common stock. 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 35,765,799 shares of common stock, 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:

9. Segment Reporting

The Company hasone 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 chief operating decision maker, or 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 for the three months ended March 31, 2026 and 2025 (in thousands):

(1) Research and development - external expenses include program expenses, 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.