X0508 4 2026-01-30 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001933852 Abdo Michael N C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATER PARKWAY DEWITT NY 13214 1 EVP and General Counsel 0 Common Stock 2026-01-30 2026-01-30 4 M 0 2287 38.02 A 9017 D Common Stock 2026-01-30 2026-01-30 4 F 0 1763 62.44 D 7254 D Common Stock 2710.425 I By 401(K) Stock Option 38.02 2026-01-30 2026-01-30 4 M 0 2287 0 D 2026-03-16 Common Stock 2287 0 D The number of shares reported herein were acquired pursuant to Community Financial System, Inc.'s 401(K) Plan and are based on a current plan statement. The option vested ratably on March 16, 2017, 2018, 2019, 2020, and 2021. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Michael N. Abdo 2026-02-03