X0508 4 2025-04-29 0000310158 Merck & Co., Inc. MRK 0001421339 DeLuca Richard R. MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY NJ 07065 1 EVP&Pres, Merck Animal Heallth 0 Common Stock 180729.7 D Common Stock - 401(k) Plan 1281.1964 I By 401(k) Restricted Stock Unit 2025-04-29 4 A 0 7555 0 A 2026-04-29 2028-04-29 Common Stock 7555 7555 D Stock Option (Right to Buy) 84.71 2025-04-29 4 A 0 34390 0 A 2026-04-29 2035-04-28 Common Stock 34390 34390 D Holdings include shares acquired in dividend reinvestment transactions. Includes shares acquired and dividends earned through April 7, 2025 in the Merck U.S. Savings Plan, a 401(k) plan. Each restricted stock unit represents a contingent right to receive one share of Merck & Co., Inc. common stock. These restricted stock units vest and are distributed as shares of Merck & Co., Inc. common stock in three equal installments on 4/29/2026, 4/29/2027 and 4/29/2028. The option vests and becomes exercisable in three equal installments on 4/29/2026, 4/29/2027 and 4/29/2028. /s/ Kelly E. W. Grez as Attorney-in-Fact for Richard R. DeLuca, Jr. 2025-05-01