SCHEDULE 13G 0001263508 XXXXXXXX LIVE Ordinary Shares, $0.01 per share 12/31/2025 0001520262 Alkermes plc. G01767105 Connaught House, 1 Burlington Road Dublin 4 L2 D04 C5Y6 Rule 13d-1(b) Baker Bros. Advisors LP DE 10012267.00 0.00 10012267.00 0.00 10012267.00 N 6.1 IA PN Baker Bros. Advisors (GP) LLC DE 10012267.00 0.00 10012267.00 0.00 10012267.00 N 6.1 HC OO Julian C. Baker X1 10012267.00 0.00 10012267.00 0.00 10012267.00 N 6.1 HC IN Felix J. Baker X1 10012267.00 0.00 10012267.00 0.00 10012267.00 N 6.1 HC IN Alkermes plc. Connaught House, 1 Burlington Road Dublin 4, L2, D04 C5Y6 This Schedule 13G is being filed jointly by Baker Bros. Advisors LP (the "Adviser"), Baker Bros. Advisors (GP) LLC (the "Adviser GP"), Julian C. Baker and Felix J. Baker (collectively, the "Reporting Persons"). The business address of each of the Reporting Persons is: c/o Baker Bros. Advisors LP 860 Washington Street, 3rd Floor New York, NY 10014 (212) 339-5690 The Adviser is a limited partnership organized under the laws of the State of Delaware. The Adviser GP is a limited liability company organized under the laws of the State of Delaware. The citizenship of each of Julian C. Baker and Felix J. Baker is the United States of America. N IA HC Items 5 through 9 and 11 of each of the cover pages to this Schedule 13G are incorporated herein by reference. Set forth below is the aggregate number of ordinary shares ("Common Stock") of Alkermes plc. (the "Issuer") directly held by each of Baker Brothers Life Sciences, L.P. ("Life Sciences") and 667, L.P. ("667", and together with Life Sciences, the "Funds") which may be deemed to be indirectly beneficially owned by the Reporting Persons. The percentage of beneficial ownership for each of the Reporting Persons reported herein and the information set forth below is based on 165,117,509 shares of Common Stock outstanding as of October 24, 2025, as reported in the Issuer's Form 10-Q filed with the Securities and Exchanges Commission ("SEC") on October 28, 2025. Such percentage figures are calculated in accordance with Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Pursuant to the management agreements, as amended, among the Adviser, the Funds and their respective general partners, the Funds' respective general partners relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds, and thus the Adviser has complete and unlimited discretion and authority with respect to the Funds' investments and voting power over investments. The Adviser GP is the sole general partner of the Adviser. The Adviser GP, Felix J. Baker and Julian C. Baker as managing members of the Adviser GP, and the Adviser may be deemed to be beneficial owners of securities of the Issuer directly held by the Funds. The Funds beneficially own 10,012,267 shares of Common Stock or 6.1% of the outstanding Common Stock. 667 beneficially owns 0.5% and Life Sciences beneficially owns 5.6% of the outstanding Common Stock. 667 directly holds 845,828 shares of Common Stock and Life Sciences directly holds 9,166,439 shares of Common Stock. 0 667 directly holds 845,828 shares of Common Stock and Life Sciences directly holds 9,166,439 shares of Common Stock. 0 Y Y N The information in Item 4 is incorporated herein by reference. Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. EXHIBIT 99.1 Joint Filing Agreement Baker Bros. Advisors LP /s/ Scott L. Lessing 02/17/2026 Baker Bros. Advisors (GP) LLC /s/ Scott L. Lessing 02/17/2026 Julian C. Baker /s/ Julian C. Baker 02/17/2026 Felix J. Baker /s/ Felix J. Baker 02/17/2026