X0609 4 2026-03-17 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001485739 Whipple John F. C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Phantom Stock (Deferred Compensation) Common Stock 5751.4337 5751.4337 D Phantom Stock (Deferred Stock Units) 0 2026-03-17 4 A 0 1220 0 A Common Stock 1220 6632.8816 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 ("DCP for Directors") will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person. Includes 44.0422 units of phantom stock acquired on January 12, 2026 as dividend equivalents 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 "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 35.9672, 40.8617, 45.1866, and 41.4544 units of phantom stock acquired on April 10, 2025, July 10, 2025, October 10, 2025, and January 12, 2026, respectively, as dividend equivalents under the Plan. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by John F. Whipple, Jr. 2026-03-18