X0609 4 2026-04-29 1 0000310158 Merck & Co., Inc. MRK 0001670690 Chattopadhyay Sanat false MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY NJ 07065 1 Exe V-P & Pres. MMD 0 Common Stock 2026-04-29 4 M 0 2597 110.03 A 16477 D Common Stock 2026-04-29 4 F 0 1130 110.03 D 15347 D Common Stock 74289 I By GRAT April 2025 Common Stock 57622 I By GRAT August 2025 Common Stock 53417 I By GRAT February 2025 Restricted Stock Unit 2026-04-29 4 M 0 2597 0 D 2026-04-29 2028-04-29 Common Stock 2597 5194 D The reporting person serves as the sole trustee of, and maintains complete investment control over, the Sanat Chattopadhyay April 2025 Grantor Retained Annuity Trust. The reporting person serves as the sole trustee of, and maintains complete investment control over, the Sanat Chattopadhyay August 2025 Grantor Retained Annuity Trust. The reporting person serves as the sole trustee of, and maintains complete investment control over, the Sanat Chattopadhyay February 2025 Grantor Retained Annuity Trust. 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. /s/ Kelly E. W. Grez as Attorney-in-Fact for Sanat Chattopadhyay 2026-05-01