X0508 4 2026-02-06 0000310158 Merck & Co., Inc. MRK 0001916310 Oosthuizen Johannes Jacobus MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY NJ 07065 1 President, U.S. Market 0 Common Stock 2026-02-06 4 S 0 15000 121.8661 D 21197.389 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $121.8200 to $121.9500, 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. /s/ Kelly E. W. Grez, as attorney-in-fact for Johannes Oosthuizen 2026-02-06