X0206 3 2026-01-01 0 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001707871 Durkee Matthew K C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 1 SVP, Chief Banking Officer President, Commercial Banking Common Stock 3257 D Common Stock 9620.2561 I By 401(K) Stock Option 54.06 2033-03-14 Common Stock 2496 D Stock Option 44.27 2034-03-19 Common Stock 5451 D Stock Option 58.10 2035-03-18 Common Stock 4474 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 options vest ratably on March 14, 2024, 2025, 2026, 2027, and 2028. The options vest ratably on March 19, 2025, 2026, 2027, 2028, and 2029. The options vest ratably on March 18, 2026, 2027, 2028, 2029, and 2030. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Matthew K. Durkee 2026-02-23