X0609 4 2026-03-19 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001475265 Pecor Raymond C III false C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 0 Common Stock 2026-03-19 4 M 0 1254 A 11439.221 D Common Stock 11277.977 I By Trust Phantom Stock (Deferred Stock Units) 2026-03-19 4 M 0 1254 D Common Stock 1254 7136.111 D On March 19, 2026, the reporting person's phantom stock units were settled for 1,254 shares of Community Financial System, Inc. common stock, and .5514 shares were settled in cash at the price of $55.61 per share. The reporting person disclaims beneficial ownership of these securities, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all of the reported shares for purposes of Section 16 or any other purpose. 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. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Raymond C. Pecor, III 2026-03-23