Form 4 Filing by John A. Vaccaro

This filing details transactions made by John A. Vaccaro, a director at Community Financial System, Inc. (CBU). On August 27, 2026, Vaccaro acquired 317 shares of Common Stock at a price of $63.11 per share, increasing his post-transaction holdings to 492 shares. The filing also reports on Vaccaro's holdings in phantom stock units, which are economically equivalent to common stock. He holds 637.367 units of Deferred Stock acquired under the Deferred Compensation Plan ("DCP for Directors") and 1228.5864 units of Phantom Stock acquired under the 2022 Long-Term Incentive Plan ("LTIP"). These phantom stock units will be settled in common stock at future dates. The dividend equivalents and reinvestment features on July 10, 2026, contributed to the phantom stock holdings.