Agenus Inc.

Item 1.01 Entry into a Material Definitive Agreement. On June 29, 2026, Agenus Inc. (the “Company”) entered into an Amendment to Notes, Extension of Warrants and Sale of New Warrants (the “Amendment”) with existing noteholders, pursuant to which the Company: • extended the maturity date of $5.09 million of senior subordinated promissory notes previously issued by the Company to such noteholders in 2015 (the “2015 Notes”) by eight months from June 20, 2026 to February 18, 2027 (all other terms of the 2015 Notes, including the applicable interest rate will remain unchanged); • extended the expiration date of all of the previously issued 2022 A Warrants held by such noteholders to purchase an aggregate of 65,000 shares of the Company’s common stock (“Common Stock”) at an exercise price of $3.25 per share to June 25, 2031 (the “Amended A Warrants”); • extended the expiration date of all of the previously issued 2022 B Warrants held by such noteholders to purchase an aggregate of 32,500 shares Common Stock at an exercise price of $3.25 per share, to June 25, 2031 (the “Amended B Warrants”); • extended the expiration date of all of the previously issued 2025 C Warrants held by such noteholders to purchase an aggregate of 67,500 shares of the Common Stock to June 25, 2031 (the “Amended C Warrants”); • issued to certain of such noteholders 2026 D Warrants to purchase an aggregate of 56,525 shares of the Common Stock at exercise price of $3.25 per share and expiring on June 25, 2031 (the “New D Warrants”); • provided that the shares of Common Stock issuable upon exercise of the New D Warrants will be registered for resale with the SEC within ninety (90) days after June 29, 2026; The foregoing descriptions of the terms of the Amendment and the New Warrants do not purport to be complete and are qualified in their entirety by reference to the text of the Amendment and the forms of the New Warrants which are filed herewith as Exhibit 4.1. A brief description of the other terms and conditions of the 2015 Notes can be found in Item 2.03 of the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission on February 26, 2015 (the “February 2025 Current Report”) and such brief description is incorporated by reference herein. The forms of the Amended A Warrant, the Amended B Warrant and the C Warrant were previously filed as Exhibits 4.1, 4.2 and 4.3, respectively, to the February 2025 Current Report. The securities issued in connection with the Amendment were issued in reliance on the exemption from registration provided by Section 4(2) of the Securities Act of 1933, as amended (the “Securities Act”), as a transaction not involving a public offering. Neither the New Warrants nor the underlying shares of common stock have been registered under the Securities Act. Neither the New Warrants nor such underlying shares of common stock may be offered or sold in the United States absent registration or an applicable exemption from registration requirements. No commission or other remuneration was paid or given directly or indirectly for soliciting such issuance.