X0609 4 2026-06-08 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001201821 STICKELS ERIC false C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 0 Common Stock 2026-06-08 4 S 0 2000 63.9811 D 31592 D Common Stock 15513.1018 I By Wife's Community Financial System, Inc. 401(k) Phantom Stock (Deferred Stock Units) Common Stock 5264.7558 5264.7558 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.72 to $64.17, inclusive. The reporting person undertakes to provide Community Financial System, Inc., any security holder of Community Financial System, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "LTIP"). Each phantom stock unit which represents a deferred stock unit is the economic equivalent of one share of Community Financial System, Inc. common stock and will be settled in common stock at a predetermined date. Includes 30.2137 units of phantom stock acquired on April 10, 2026 under the Plan's dividend reinvestment feature. Danielle M. Cima, pursuant to a Confirming Statement executed by Eric E. Stickels 2026-06-10