X0508 4 2024-11-06 0000723188 COMMUNITY FINANCIAL SYSTEM, INC. CBU 0001486056 Bolus Mark J. C/O COMMUNITY FINANCIAL SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Common Stock 2024-11-06 4 M 0 2123 38.02 A 101050.55 D Common Stock 2024-11-06 4 M 0 1969 35.36 A 103019.55 D Common Stock 2024-11-06 4 S 0 2192 69.5407 D 100827.55 D Common Stock 2024-11-06 4 S 0 1900 70.6592 D 98927.55 D Stock Option 38.02 2024-11-06 4 M 0 2123 0 D 2016-03-16 2026-03-16 Common Stock 2123 0 D Stock Option 35.36 2024-11-06 4 M 0 1969 0 D 2015-03-18 2025-03-18 Common Stock 1969 0 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $69.15 to $70.03, 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 price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $70.50 to $70.945, 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 Mark J. Bolus 2024-11-07