X0609 4 2026-03-17 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001738659 Singh Savneet C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Deferred Stock (Deferred Compensation) Common Stock 1376.6175 1376.6175 D Phantom Stock (Deferred Stock Units) 2026-03-17 4 A 0 1220 0 A Common Stock 1220 2474.5514 D 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 for Directors (the "DCP for Directors"), will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person. Includes 7.8928 units of phantom stock acquired as dividend equivalents on January 12, 2026 under the DCP for Directors. The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "LTIP"). 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 9.6079 units of phantom stock acquired on January 12, 2026 under the LTIP's dividend reinvestment feature. /s/ Danielle M. Cima, pursuant to Confirming Statement executed by Savneet Singh 2026-03-18