X0508 4 2025-05-19 0000354190 Arthur J. Gallagher & Co. AJG 0001386997 Pietrucha Susan E 2850 GOLF ROAD ROLLING MEADOWS IL 60008-4002 1 Chief Human Resources Officer 0 Common Stock 2025-05-19 4 M 0 13500 79.59 A 25440.8404 D Common Stock 2025-05-19 4 S 0 13500 344.128 D 11940.8404 D Common Stock 294.872 I Gallagher 401(k) plan account Non-qualified Stock Option 79.59 2025-05-19 4 M 0 13500 0 D 2026-03-14 Common Stock 13500 0 D The price reported is an average weighted price. The shares were sold in multiple transactions on 5/19/2025 at prices ranging from $344.00 to $344.49. The reporting person will provide to the Securities and Exchange Commission staff, the issuer, or any security holder of the issuer, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in the footnotes to this Form 4. One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date. /s/ Monica Norzagaray, by power of attorney 2025-05-20