X0508 4 2026-03-02 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001707871 Durkee Matthew K C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 1 SVP, Chief Banking Officer President, Commercial Banking 0 Common Stock 2026-03-02 4 F 0 399 60.55 D 2858 D Common Stock 9743.697 I By 401(K) Payment of tax liability associated with vesting of restricted stock award. 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. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Matthew K. Durkee 2026-03-03