X0508 4 2026-03-04 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001866135 Karaivanov Dimitar C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 1 President & CEO 0 Common Stock 2026-03-04 4 A 0 5224.2062 0 A 26482.2062 D Common Stock 2026-03-04 4 F 0 2825.2062 59.87 D 23657 D Common Stock 3271.3426 I By 401(k) Plan 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 4,698 shares of common stock under the award and 526.2062 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 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 Dimitar Karaivanov 2026-03-06