X0202 SCHEDULE 13D/A 0000950157-26-000478 0000875045 XXXXXXXX LIVE 1 Common Stock, par value $0.0001 per share 05/14/2026 false 0001492422 03753U106 Apellis Pharmaceuticals, Inc.

100 Fifth Avenue Waltham MA 02451

Wendell Taylor, Secretary (617) 679-2000 225 Binney Street Cambridge MA 02142 0000875045 N Biogen Inc. b OO N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 CO This Amendment No. 1 to Schedule 13D (this "Amendment") relates to the common stock, par value $0.0001 per share (the "Shares"), of Apellis Pharmaceuticals, Inc., a Delaware corporation ("Apellis") and amends and supplements the statement on Schedule 13D originally filed by Biogen Inc., a Delaware corporation ("Biogen"), on April 6, 2026 (the "Prior Schedule 13D"). The filing of this Amendment represents the final amendment to the Prior Schedule 13D and constitutes an exit filing for the Reporting Person. Except as otherwise specified in this Amendment, all items left blank remain unchanged in all material respects and any items that are reported are deemed to amend and restate the corresponding items in the Prior Schedule 13D. Unless otherwise indicated, all capitalized terms used herein but not defined herein shall have the same meanings ascribed to them in the Prior Schedule 13D. Common Stock, par value $0.0001 per share Apellis Pharmaceuticals, Inc. 100 Fifth Avenue Waltham MA 02451 Item 4 of the Prior Schedule 13D is hereby amended and supplemented by adding the following at the end thereof: As previously disclosed, on March 31, 2026, Biogen entered into an Agreement and Plan of Merger (the "Merger Agreement") with Apellis and Aspen Purchaser Sub, Inc., a Delaware corporation and a wholly owned subsidiary of Biogen ("Purchaser"). Pursuant to the Merger Agreement, on April 14, 2026, Purchaser commenced a tender offer (the "Offer") to acquire any and all outstanding Shares, in exchange for (i) $41.00 per Share, net to the seller in cash, without interest and subject to reduction for any applicable tax withholding (the "Cash Amount"), plus (ii) one contractual, non-transferable contingent value right per Share (each, a "CVR") representing the right to receive contingent cash payments of up to an aggregate of $4.00 in cash, without interest and subject to reduction for any applicable tax withholding, upon the achievement of certain specified milestones, in each case upon the terms and subject to the conditions set forth in the Offer to Purchase, dated April 14, 2026 (as amended or supplemented from time to time, the "Offer to Purchase") and in the related Letter of Transmittal. As a result of the satisfaction of the Minimum Condition (as defined in the Offer) and each of the other conditions to the Offer, on May 14, 2026, Purchaser irrevocably accepted for payment all Shares that were validly tendered (and not validly withdrawn) pursuant to the Offer. Following the completion of the Offer, on May 14, 2026, pursuant to the terms of the Merger Agreement, Purchaser merged with and into Apellis, without a vote of the stockholders of Apellis in accordance with Section 251(h) of the General Corporation Law of the State of Delaware, with Apellis continuing as the surviving corporation of the merger and as a wholly owned subsidiary of Biogen (the "Merger"). Items 5(a), (b) and (e) of the Prior Schedule 13D are hereby amended and supplemented by adding the following at the end thereof: On May 14, 2026, the Merger was consummated and Purchaser was merged with and into Apellis, with Apellis surviving the Merger as a wholly owned subsidiary of Biogen. Upon the consummation of the Merger, the Tender and Support Agreement automatically terminated pursuant to its terms and is of no further force or effect. Biogen Inc. /s/ Wendell Taylor 05/14/2026