X0609 4 2026-03-19 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0002009605 Sullivan Michele C/O COMMUNITY FINANCIAL SYSTEM, INC. 333 BUTTERNUT DRIVE SYRACUSE NY 13214 1 0 Deferred Stock (Deferred Compensation) 2026-03-19 4 A 0 447.3116 55.61 A Common Stock 447.3116 3530.456 D Each unit of phantom stock is the economic equivalent of one share of Community Financial System, Inc. common stock. The units of phantom stock relating to the Deferred Compensation Plan for Directors (the "DCP for Directors"), will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person. /s/ Danielle M. Cima, pursuant to Confirming Statement executed by Michele Sullivan 2026-03-19