AnaptysBio, Inc.

Item 1.01 Entry into a Material Definitive Agreement. On March 26, 2026, First Tracks Biotherapeutics and EcoR1 Capital Fund Qualified, L.P. (the “Selling Stockholder”) entered into a purchase agreement (the “Purchase Agreement”) with certain third party investors (collectively, the “Investors”), pursuant to which SpinCo agreed to issue and sell an aggregate 5,791,478 shares of SpinCo’s common stock, par value $0.001 per share (the “Common Stock”) (collectively, the “Primary Shares”), and the Selling Stockholder agreed to sell an aggregate of 4,705,576 shares of Common Stock that the Selling Stockholder will receive in the previously announced Spin-Off of SpinCo from AnaptysBio (the “Secondary Shares” and, together with the Primary Shares, the “Purchased Securities”) to the Investors, at a purchase price of $13.81 per share (the “Private Placement”). The aggregate gross proceeds to First Tracks Biotherapeutics from the sale of the Primary Shares is expected to be approximately $80 million, before deducting offering expenses. First Tracks Biotherapeutics will not receive any proceeds from the sale of the Secondary Shares. The Private Placement is expected to close subject to, and immediately after, the previously announced separation of SpinCo from AnaptysBio, which is expected to occur on April 20, 2026. The Purchase Agreement contains customary representations, warranties and agreements by SpinCo and the Selling Stockholder, customary indemnification obligations of SpinCo and the Selling Stockholder to the Investors and other obligations of the parties. In accordance with the Purchase Agreement, the closing of the Private Placement (the “Closing”) is subject to the satisfaction or waiver of certain conditions, including, among others, the effectiveness of the registration statement on Form 10, initially filed with the SEC on March 3, 2026 (as amended, the “Registration Statement”), the completion of the distribution of SpinCo shares substantially on the terms described in that certain Separation and Distribution Agreement, the form of which was filed as Exhibit 2.1 to the Registration Statement, the listing of the Common Stock on the Nasdaq Stock Market LLC (“Nasdaq”), the absence of any material adverse effect on SpinCo since the date of the Purchase Agreement, and other customary closing conditions. In connection with the Private Placement, SpinCo will enter into a registration rights agreement (the “Registration Rights Agreement”) with the Investors at the Closing, pursuant to which SpinCo will be required to file a registration statement with the SEC covering the resale by the Investors of their shares of Common Stock as promptly as reasonably practicable, and in any event no later than 45 days, following the closing of the Private Placement. Neither this Current Report on Form 8-K, nor the exhibits attached hereto, is an offer to sell or the solicitation of an offer to buy the securities described herein. The foregoing descriptions of the Purchase Agreement and Registration Rights Agreement do not purport to be complete and are qualified in their entirety by reference to the Purchase Agreement and Form of Registration Rights Agreement filed as Exhibits 10.1 and 10.2 to this Current Report on Form 8-K and incorporated herein by reference. A copy of the Purchase Agreement has been included as an exhibit to this Current Report on Form 8-K to provide investors with information regarding its terms. It is not intended to provide any other factual information about First Tracks Biotherapeutics. The representations, warranties and covenants contained in the Purchase Agreement were made only for purposes of that agreement and as of specific dates; were made solely for the benefit of the parties to the Purchase Agreement; may be subject to limitations agreed upon by the contracting parties, including being qualified by confidential disclosures; may not have been intended to be statements of fact, but rather, as a method of allocating contractual risk and governing the contractual rights and relationships between the parties to the Purchase Agreement; and may be subject to standards of materiality applicable to contracting parties that differ from those applicable to investors. Investors should not rely on the representations, warranties and covenants or any descriptions thereof as characterizations of the actual state of facts or condition of First Tracks Biotherapeutics. Moreover, information concerning the subject matter of the representations, warranties and covenants may change after the date of the Purchase Agreement, which subsequent information may or may not be fully reflected in First Tracks Biotherapeutics’ public disclosures.

Item 1.02 Termination of a Material Definitive Agreement. As previously disclosed, on November 5, 2024, the Company entered into a Sales Agreement (the “Sales Agreement”) with TD Securities (USA) LLC (the “Agent”), pursuant to which the Company could issue and sell, from time to time, shares of its common stock, par value $0.001 per share (the “Common Shares”), up to an aggregate offering price equal to the Maximum Amount (the “ATM Program”). The Company has issued a termination letter to the Agent to terminate the Sales Agreement. Following the termination of the Sales Agreement, the Company may not offer or sell any additional Common Shares under the Sales Agreement. The foregoing description of the Sales Agreement is not complete and is qualified in its entirety by reference to the full text of the Sales Agreement, a copy of which was filed as Exhibit 1.2 to Registration Statement on Form S-3 filed with the Securities and Exchange Commission on November 5, 2024.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. Appointment of Director On March 26, 2026, the Board appointed Susannah Gray as a Class I director, a member of the Nominating and Corporate Governance Committee and a member of the Research and Development Committee, effective immediately. In connection with her appointment as a non-employee director of the Board, Ms. Gray will receive an initial grant following the Spin-Off including (i) pro rata portion of the annual retainer for service as a director for the remaining portion of the year, and (ii) 11,250 restricted stock units, which shall vest over a three-year period, in each case subject to Ms. Gray’s continued service to the Company. The Company has entered into its standard form of indemnification agreement with Ms. Gray. The form of the indemnification agreement was previously filed by the Company as Exhibit 10.1 to the Company’s Registration Statement on Form S-1 filed with the Securities and Exchange Commission on September 9, 2015 and is incorporated by reference herein. There are no arrangements or understandings between Ms. Gray and any other persons, pursuant to which Ms. Gray was selected as a member of the Board. There are also no family relationships among any of the Company’s other directors or executive officers and Ms. Gray, and Ms. Gray does not have any direct or indirect material interest in any transaction required to be disclosed pursuant to Item 404(a) of Regulation S-K. Executive Officer Transitions On March 26, 2026, Dennis Mulroy and AnaptysBio entered into a transition and separation agreement (the “Mulroy Separation Agreement”), conditioned upon and effective on the separation of SpinCo from AnaptysBio, which is expected to occur on April 20, 2026. The Mulroy Separation Agreement provides that, among other things, the Mulroy Employment Agreement was terminated, and in exchange for executing a general release of claims in favor of the Company, Mr. Mulroy will receive a lump sum payment equal to nine months of base pay and reimbursement for his COBRA premiums for a period of 9 months. Mr. Mulroy is also expected to enter into a consulting agreement with First Tracks Biotherapeutics following the Spin-Off. The foregoing description of the Mulroy Separation Agreement is qualified in its entirety by reference to the full text of the Mulroy Separation Agreement, which will be filed an exhibit to the Company’s Quarterly Report on Form 10-Q for the three months ended March 31, 2026. On March 26, 2026, Eric Loumeau and AnaptysBio entered into a transition and separation agreement (the “Loumeau Separation Agreement”), conditioned upon and effective on the separation of SpinCo from AnaptysBio, which is expected to occur on April 20, 2026. The Loumeau Separation Agreement provides that, among other things, the Loumeau Employment Agreement was terminated, and in exchange for executing a general release of claims in favor of the Company, Mr. Loumeau will receive a lump sum payment equal to nine months of base pay and reimbursement for his COBRA premiums for a period of 9 months. Mr. Loumeau is also expected to enter into consulting agreements with both the Company and First Tracks Biotherapeutics following the Spin-Off. The foregoing description of the Loumeau Separation Agreement is qualified in its entirety by reference to the full text of the Loumeau Separation Agreement, which will be filed as an exhibit to the Company’s Quarterly Report on Form 10-Q for the three months ended March 31, 2026.

Item 7.01 Regulation FD. Spin-Off First Tracks Biotherapeutics previously filed the Registration Statement. The Registration Statement includes a preliminary information statement that describes the Spin-Off and provides important information regarding SpinCo’s business and management. On March 27, 2026, in connection with the previously announced Spin-Off, the Board announced that the Company will distribute all of the outstanding shares of Common Stock of SpinCo to holders of shares of the Company’s common stock as a pro rata dividend prior to the U.S. market open on April 20, 2026. The Common Stock of SpinCo is expected to begin trading on Nasdaq on April 20, 2026 under the ticker “TRAX.” Holders of the Company’s common stock will be entitled to receive one share of SpinCo Common Stock for every share of the Company’s common stock held on April 6, 2026, the record date for the distribution. The distribution is subject to the satisfaction or waiver of certain conditions. A copy of the press release is attached as Exhibit 99.1 and incorporated into this Item 7.01 by reference. First Tracks Private Placement On March 27, 2026, the Company issued a press release announcing the Private Placement, a copy of which is attached hereto as Exhibit 99.2 and is incorporated into this Item 7.01 by reference. Stock Buyback Program On March 27, 2026, the Company issued a press release announcing that the Board has authorized a stock repurchase plan (the “Stock Repurchase Plan”), under which the Company may repurchase up to $100.0 million of the Company’s outstanding common stock, par value $0.001 per share. A copy of the press release is attached as Exhibit 99.3 to this Current Report on Form 8-K and is incorporated into this Item 7.01 by reference. The information furnished in Item 7.01, including Exhibits 99.1, 99.2 and 99.3, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section, and shall not be deemed to be incorporated by reference into any filing of the Company under the Exchange Act or the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.