X0609 4 2026-03-17 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001794595 MacPherson Kerrie D. C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Phantom Stock (Deferred Stock Units) 2026-03-17 4 A 0 1220 0 A Common Stock 1220 7630.8867 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 44.5994, 48.3956, 53.5179, and 49.0975 units of phantom stock acquired as dividend equivalents on April 10, 2025, July 10, 2025, October 10, 2025, and January 12, 2026, respectively, under the LTIP. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Kerrie D. MacPherson 2026-03-18