X0508 4 2026-03-04 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001933852 Abdo Michael N C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 EVP and General Counsel 0 Common Stock 2026-03-04 4 A 0 1948.2353 0 A 8717.2353 D Common Stock 2026-03-04 4 F 0 707.2353 59.87 D 8010 D Common Stock 2731.4068 I By 401(K) On March 4, 2026, the Compensation Committee approved the vesting of the three-year performance-based restricted stock award, granted to the reporting person in 2023, based on achievement of predetermined performance criteria at the target level. The reporting person received 1,752 shares of common stock under the award and 196.2353 shares of common stock acquired under the dividend reinvestment feature of the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan"). Payment of tax liability associated with vesting of performance stock award. The number of shares reported herein were acquired pursuant to Community Financial System, Inc.'s 401(K) Plan and are based on a current plan statement. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Michael N. Abdo 2026-03-06