X0508 4 2025-03-18 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001485738 Fesette Neil E. C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Common Stock 10986.059 D Phantom Stock (Deferred Compensation) Common Stock 6700.7282 6700.7282 D Phantom Stock (Deferred Stock Units) 2025-03-18 4 A 0 1225 0 A Common Stock 1225 6841.1314 D Includes 85.436, 78.792, 67.829, and 64.3948 shares acquired on April 10, 2024, July 10, 2024, October 10, 2024, and January 10, 2025, respectively, pursuant to the Community Financial System, Inc. Dividend Reinvestment Plan. Each unit of phantom stock is the economic equivalent of one share of Community Financial System, Inc. common stock. The units of phantom stock relating to the Deferred Compensation Plan will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person. Includes 73.1278, 66.7518, 57.446, and 64.5001 units of phantom stock acquired as dividend equivalents on April 10, 2024, July 10, 2024, October 10, 2024, and January 10, 2025, respectively, under the Deferred Compensation Plan. The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan"). Each phantom stock unit which represents a deferred stock unit is the economic equivalent of one share of Community Financial System, Inc. common stock and will be settled in common stock at a predetermined date. Includes 35.5319, 45.4658, 39.1283, and 31.3024 units of phantom stock acquired as dividend equivalents on April 10, 2024, July 10, 2024, October 10, 2024, and January 10, 2025, respectively, under the Plan. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Neil E. Fesette 2025-03-20