BIIB: Material agreement · Acquisition or asset disposal · New financial obligation · Company disclosure

Item 1.01 Entry into a Material Definitive Agreement. CVR Agreement As previously disclosed, on March 31, 2026, Biogen Inc., a Delaware corporation (“Biogen”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Apellis Pharmaceuticals, Inc., a Delaware corporation (“Apellis”), and Aspen Purchaser Sub, Inc., a Delaware corporation and a wholly owned subsidiary of Biogen (“Purchaser”). Pursuant to the Merger Agreement and in connection with the irrevocable acceptance for payment by Purchaser of all outstanding shares of common stock, par value $0.0001 per share, of Apellis (the “Shares”) validly tendered and not validly withdrawn pursuant to the Offer (as defined below), on May 14, 2026, Biogen, Apellis and Equiniti Trust Company, LLC, a New York limited liability trust company, entered into a Contingent Value Rights Agreement (the “CVR Agreement”) governing the terms of the CVRs (as defined below) issued pursuant to the Offer and the Merger (as defined below). Each CVR represents a non-transferable contractual contingent right to receive the following cash payments, without interest and subject to reduction for any applicable tax withholding (the “Milestone Payments”) if the following milestones (each, a “Milestone”) are achieved: • $2.00 per CVR, upon the achievement of Annual Net Sales (as defined in the CVR Agreement) of at least $1,500,000,000 attributable to SYFOVRE® and related products in the aggregate during the 2027, 2028, 2029 or 2030 calendar years (the “Net Sales Milestone 1”); and • $2.00 per CVR, upon the achievement of Annual Net Sales (as defined in the CVR Agreement) of at least $2,000,000,000 attributable to SYFOVRE® and related products in the aggregate during the 2027, 2028, 2029, 2030 or 2031 calendar years (the “Net Sales Mil