X0508 4 2026-02-04 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001485739 Whipple John F. C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Common Stock 2026-02-04 4 M 0 4246 38.02 A 12752.0302 D Common Stock 2026-02-04 4 S 0 4246 65.1681 D 8506.0302 D Stock Option 38.02 2026-02-04 4 M 0 4246 0 D 2016-03-16 2026-03-16 Common Stock 4246 0 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $65.00 to $65.355, 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. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by John F. Whipple, Jr. 2026-02-06