Entry into a Material Definitive Agreement. CVR Agreement Pursuant to the Merger Agreement and in connection with the irrevocable acceptance for payment by Purchaser of all outstanding Shares validly tendered and not validly withdrawn pursuant to the Offer, on May 14, 2026, Biogen, the Company and Equiniti entered into the CVR Agreement. Each CVR represents a non-transferable contractual contingent right to receive the following cash payments, without interest and subject to reduction for any…

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing. On May 13, 2026, the Company (i) notified The Nasdaq Stock Market (“Nasdaq”) of the anticipated consummation of the Merger and (ii) requested that Nasdaq (x) suspend trading of the Shares, effective at 8:00 p.m., Eastern Time, on May 13, 2026, and, following the Effective Time, (y) file with the U.S. Securities and Exchange Commission (the “SEC”) a Form 25, Notification of Removal from Listing…

Termination of a Material Definitive Agreement In connection with the consummation of the Merger, effective as of immediately prior to the Effective Time, the Company terminated its 2017 Employee Stock Purchase Plan. In connection with the consummation of the Merger, and concurrently with the Effective Time, the Company terminated all commitments outstanding under, and repaid all outstanding loans and other amounts due under, the Financing Agreement, dated as of June 30, 2025 (and as further…

Changes in Control of Registrant. As a result of the consummation of the Offer and the Merger, on May 14, 2026, a change in control of the Company occurred, and the Company is now a wholly owned subsidiary of Biogen. The information set forth in the Introductory Note, Item 2.01,

Director — Mikael Dolsten, Paul Fonteyne, Stephanie Monaghan O’Brien, A. Sinclair Dunlop, Alec Machiels, Keli Walbert, Gerald Chan, Cedric Francois, Craig Wheeler: The resignations were a result of the Merger and not due to any disagreement.

Completion of Acquisition or Disposition of Assets. The information set forth in the Introductory Note and

Material Modification to Rights of Security Holders. The information set forth in the Introductory Note, Item 3.01,

The filing describes an amendment to the executive separation benefits and retention plan in connection with a merger.

Other Events. Press Release On March 31, 2026, the Company and Parent issued a joint press release announcing the entry into the Merger Agreement. A copy of the press release is attached as Exhibit 99.2 hereto and is incorporated herein by reference. Cautionary Note Regarding Forward-Looking Statements This Current Report on Form 8-K contains “forward-looking” statements that are subject to risks, uncertainties and other factors relating to future events and the future performance of Biogen I…

The filing describes a compensatory plan related to potential excise taxes post-merger, not a management change.

Entry into a Material Definitive Agreement. Agreement and Plan of Merger On March 31, 2026, Apellis Pharmaceuticals, Inc., a Delaware corporation (the “Company”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Biogen Inc., a Delaware corporation (“Parent”), and Aspen Purchaser Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Parent (“Purchaser”). Pursuant to the Merger Agreement, and upon the terms and subject to the conditions therein, Pur…

Director — Mikael Dolsten, M.D., Ph.D.: Dr. Dolsten was elected to the Board as a Class I director.

Results of Operations and Financial Condition. On January 12, 2026, Apellis Pharmaceuticals, Inc. (the “Company”) issued a press release announcing preliminary unaudited total U.S. net product revenues and net product revenues for SYFOVRE and EMPAVELI for the fourth quarter and full year ended December 31, 2025 and its cash and cash equivalents as of December 31, 2025. The full text of the press release issued by the Company in connection with the announcement is being furnished as Exhibit 99…

Entry into a Material Definitive Agreement. On July 1, 2025 (the “Closing Date”), Apellis Pharmaceuticals, Inc. and its subsidiaries Apellis International GmbH and APL DEL Holdings, LLC (collectively, the “Company”) entered into a Royalty Buy-Down Agreement (the “Royalty Agreement”) with Swedish Orphan Biovitrum AB (Publ) (“Sobi”). Under the Royalty Agreement, Sobi agreed to pay the Company an upfront payment of $275 million within five business days after the Closing Date, and up to an aggre…

Director — Craig A. Wheeler: The filing discloses the routine election of a new independent director to the Board of Directors, which is a standard governance event and not an executive departure.

Director — Keli Walbert: The filing discloses the routine election of a new independent director to the Board of Directors, which is a standard governance event and not an executive departure.

Results of Operations and Financial Condition. On January 13, 2025, Apellis Pharmaceuticals, Inc. (the “Company”) issued a press release announcing preliminary unaudited total U.S. net product revenues and net product revenues for SYFOVRE and EMPAVELI for the fourth quarter and full year ended December 31, 2024 and its cash and cash equivalents as of December 31, 2024. The full text of the press release issued by the Company in connection with the announcement is being furnished as Exhibit 99…

Other Events. On August 8, 2024, Apellis Pharmaceuticals, Inc. (“Apellis”) and Sobi ® announced positive topline results from the Phase 3 VALIANT study investigating systemic pegcetacoplan in patients with C3 glomerulopathy (C3G) or primary immune complex membranoproliferative glomerulonephritis (IC-MPGN), which are rare kidney diseases with no approved treatments. The study met the primary endpoint, demonstrating a statistically significant and clinically meaningful 68% (p<0.0001) proteinuri…

Entry into a Material Definitive Agreement. On May 13, 2024 (the “Closing Date”), Apellis Pharmaceuticals, Inc. (the “Company”) entered into a financing agreement (the “Financing Agreement”) with the guarantors party thereto, the lenders party thereto (the “Lenders”), and Sixth Street Lending Partners, as the administrative agent and collateral agent for the Lenders. The Financing Agreement provides for a senior secured term loan facility of up to $475 million (the “Credit Facility”), consist…

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. Apellis Pharmaceuticals, Inc. Date: May 14, 2024 By: /s/ Timothy Sullivan Timothy Sullivan Chief Financial Officer