1. Description of the Business

AnaptysBio, Inc. (“we,” “us,” “our,” or the “Company”) was incorporated in the state of Delaware in November 2005. Prior to the separation described below, we were a clinical-stage biotechnology company focused on delivering innovative immunology therapeutics for autoimmune and inflammatory diseases. Our clinical-stage pipeline included ANB033, rosnilimab and ANB101. We also discovered and out-licensed, in financial collaborations, multiple therapeutic antibodies, including a PD-1 antagonist (Jemperli (dostarlimab-gxly) or “Jemperli”) to GSK and an IL-36R antagonist (“Quimilza”) to Vanda Pharmaceuticals Inc. (“Vanda”). We recognize revenue from milestones and royalties achieved under our immuno-oncology collaboration with GSK and license and transition services revenue from our collaboration with Vanda.

Our management believes our currently available resources will provide sufficient funds to enable us to meet our operating plans for at least the next 12 months from the issuance of our consolidated financial statements. The accompanying consolidated financial statements do not include any adjustments that might be necessary if we are unable to continue as a going concern.

First Tracks Biotherapeutics Separation

In September 2025, we announced that our board of directors (“Board of Directors”) approved plans to explore separating our business into two independent, publicly traded companies. We would hold and continue to manage the financial collaboration for Jemperli with GSK and for Quimilza with Vanda, with a focus on protecting and returning value of the royalties to its stockholders. The spun-out company is a clinical-stage biotechnology company focused on the development and potential commercialization of innovative therapeutics for autoimmune and inflammatory diseases, including ANB033, rosnilimab and ANB101. This separation (the “Spin-Off”) was completed on April 20, 2026.

The Spin-Off of First Tracks Biotherapeutics, Inc. (“First Tracks Biotherapeutics”) was achieved through our pro rata distribution of 29,100,902 shares of common stock of First Tracks Biotherapeutics to holders of record of our common stock. Each holder of record of our common stock received one share of First Tracks Biotherapeutics’ common stock for every one share of our common stock held on April 6, 2026, the record date for the distribution.

In connection with the Spin-Off, we entered into a separation and distribution agreement (the “Separation and Distribution Agreement”) with First Tracks Biotherapeutics. The Separation and Distribution Agreement identifies the assets transferred to (including the contracts assigned) or retained by, and the liabilities assumed or retained by, each of us and First Tracks Biotherapeutics. Pursuant to the Separation and Distribution Agreement, on the Distribution Date, $100 million in cash and cash equivalents was allocated to First Tracks Biotherapeutics from us. Furthermore, all accounts payable and accrued liabilities were assumed by us. The results of First Tracks Biotherapeutics are included within discontinued operations in our consolidated financial statements. See Note 12 for further details.

Change in Fiscal Year End

On May 18, 2026, the Board of Directors approved a change to the Company’s fiscal year end from December 31 to June 30, resulting in a six-month transition period from January 1, 2026 to June 30, 2026 (the “Transition Period”). As a result of this change, we are filing this Transition Report on Form 10-KT for the six-month period ended June 30, 2026, pursuant to Rule 15d-10(e)(2) of the Exchange Act.