X0609 4 2026-09-09 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001738659 Singh Savneet false C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 0 Common Stock 2026-09-09 4 P 0 400 62.47 A 418 D Deferred Stock (Deferred Compensation) Common Stock 1396.7397 1396.7397 D Phantom Stock (Deferred Stock Units) Common Stock 2501.4755 2501.4755 D The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $62.41 to $62.53, inclusive. The reporting person undertakes to provide Community Financial System, Inc., any security holder of Community Financial System, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote. 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 10.3606 and 9.7616 units of phantom stock acquired as dividend equivalents on April 10, 2026, and July 10, 2026, respectively, 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 9.4416 and 17.4825 units of phantom stock acquired on April 10, 2026, and July 10, 2026, respectively, under the LTIP's dividend reinvestment feature. /s/ Danielle M. Cima, pursuant to Confirming Statement executed by Savneet Singh 2026-09-10