Aptevo Therapeutics Inc.

Item 1.01 Entry into a Material Definitive Agreement. On October 23, 2026, Aptevo Therapeutics Inc. (the "Company") entered into Amendment No. 6 (the "Amendment") to the Rights Agreement, dated as of November 8, 2020, between the Company and Broadridge Corporate Issuer Solutions, LLC, as rights agent (as amended and/or restated from time to time, the "Rights Agreement"). The Rights Agreement pertains to those certain contingent rights to purchase one one-thousandth of a share of Series A Junior Participating Preferred Stock, par value $0.001, of the Company (each, a "Preferred Share"). The Amendment extends the definition of "Final Expiration Date" (as defined in the Rights Agreement) and certain related language in the Rights Agreement to October 23, 2027. The Amendment also changes the definition of "Purchase Price" (as defined in the Rights Agreement) and certain related language in the Rights Agreement to $14.56 per one one-thousandth of a Preferred Share. The foregoing description of the Amendment does not purport to be complete and is qualified in its entirety by reference to the complete text of the Amendment, a copy of which is attached as Exhibit 4.1 to this Current Report on Form 8-K and incorporated herein by reference. Item 3.03 Material Modification to Rights of Security Holders. The information set forth under "Item 1.01 Entry into a Material Definitive Agreement" of this Current Report on Form 8-K is incorporated into this Item 3.03 by reference. Item 9.01 Financial Statements and Exhibits. (d) Exhibits

4.1 Amendment No. 6 to Rights Agreement, dated as of October 23, 2026, between the Company and Broadridge Corporate Issuer Solutions, LLC, as Rights Agent

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