X0508 4 2026-02-09 0000310158 Merck & Co., Inc. MRK 0001737231 Zachary Jennifer MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY NJ 07065 1 EVP, General Counsel 0 Common Stock 2026-02-09 4 M 0 25946 119.1522 A 94861.671 D Common Stock 2026-02-09 4 S 0 25946 119.1522 D 68915.671 D Common Stock 2026-02-09 4 M 0 56792 119.1522 A 125707.671 D Common Stock 2026-02-09 4 S 0 56792 119.1522 D 68915.671 D Common Stock 2026-02-09 4 M 0 38835 119.1522 A 107750.671 D Common Stock 2026-02-09 4 S 0 38835 119.1522 D 68915.671 D Stock Option (Right to Buy) 75.36 2026-02-09 4 M 0 25946 0 D 2021-05-01 2030-04-30 Common Stock 25946 0 D Stock Option (Right to Buy) 73.73 2026-02-09 4 M 0 56792 0 D 2022-05-04 2031-05-03 Common Stock 56792 0 D Stock Option (Right to Buy) 87.10 2026-02-09 4 M 0 38835 0 D 2023-05-03 2032-05-02 Common Stock 38835 0 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $118.9600 to $119.5100, inclusive. The reporting person undertakes to provide to Merck & Co., Inc., any security holder of Merck & Co., Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above in this footnote. The option vested and became exercisable in three equal installments on 5/1/2021, 5/1/2022 and 5/1/2023. The option vests and becomes exercisable in three equal installments on 5/4/2022, 5/4/2023 and 5/4/2024. The option vests and becomes exercisable in equal installments on 5/3/2023, 5/3/2024 and 5/3/2025. /s/ Kelly E. W. Grez as Attorney-in-Fact for Jennifer Zachary 2026-02-09