X0508 4 2024-03-19 0000723188 COMMUNITY BANK SYSTEM, INC. CBU 0001485739 Whipple John F. C/O COMMUNITY BANK SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Phantom Stock (Deferred Stock Units) 0 2024-03-19 4 A 0 1395 0 A Common Stock 1395 3898.9969 D The reporting person has received deferred stock units under the Community Bank 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 Bank System, Inc. common stock and will be settled in common stock at a predetermined date. Includes 21.3781, 24.0768, 25.9359, and 22.2249 units of phantom stock acquired on April 10, 2023, July 10, 2023, October 10, 2023, and January 10, 2024, respectively, as dividend equivalents under the Plan. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by John F. Whipple, Jr. 2024-03-20