X0609 4 2026-03-31 0000310158 Merck & Co., Inc. MRK 0001805745 Seidman Christine E false MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY NJ 07065 1 0 Common Stock 100 D Phantom Stock 2026-03-31 4 A 0 67.5451 120.29 A Common Stock 67.5451 19238.3277 D 1-for-1 Phantom stock units are to be settled 100% in cash upon reporting person's termination of service in accordance with a distribution schedule elected pursuant to the terms of the Plan for Deferred Payment of Directors' Compensation. Holdings include shares acquired in dividend reinvestment transactions. /s/ Kelly E. W. Grez as Attorney-in-Fact for Christine E. Seidman 2026-04-01