Annexon, Inc.

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.

• 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.

“At the Market” Equity Offering Program

On March 30, 2026, we entered into the Sales Agreement with TD Cowen as sales agent, pursuant to which we may offer and sell, from time to time through TD Cowen, at our option, shares of our common stock having an aggregate offering price of up to $150.0 million.

The sales of shares of our common stock will be made by any method permitted that is deemed to be an “at-the-market” equity offering as defined in Rule 415(a)(4) promulgated under the Securities Act, including sales made directly on or through the Nasdaq Global Select Market. We agreed to pay TD Cowen a commission of up to 3.0% of the aggregate gross proceeds from any shares of our common stock sold by TD Cowen pursuant to the Sales Agreement.

The foregoing description of the Sales Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Sales Agreement, a copy of which is filed as Exhibit 10.16 to this Annual Report on Form 10-K.

The foregoing disclosure shall not constitute an offer to sell or the solicitation of an offer to buy the securities discussed herein, nor shall there be any offer, solicitation, or sale of the securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.