CBU · Community Financial System, Inc. · Insider Trading

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.

Includes 25.0107 units of phantom stock acquired on July 10, 2026 as dividend equivalents under the DCP for Directors.

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 ("DCP for Directors") will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $62.41 to $62.53, 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 purchased 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 purchased in multiple transactions at prices ranging from $63.1899 to $63.5989, 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 purchased at each separate price within the range set forth in this footnote.

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 ("DCP for Directors") will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person.

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.

Includes 23.2041 units of phantom stock acquired as dividend equivalents on April 10, 2026 under the DCP for Directors.

The option vests ratably on March 19, 2025, 2026, 2027, 2028, and 2029.

The option vested ratably on March 17, 2021, 2022, 2023, 2024, and 2025.

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.

Payment of tax liability associated with vesting of restricted stock award.

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.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

Includes 54.1540 units of phantom stock acquired on April 10, 2026 under the LTIP's dividend reinvestment feature.

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.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

Includes 9.4418 units of phantom stock acquired on April 10, 2026 under the LTIP's dividend reinvestment feature.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

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.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

Includes 9.4418 units of phantom stock acquired on April 10, 2026 under the LTIP's dividend reinvestment feature.

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.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

Includes 9.4418 units of phantom stock acquired on April 10, 2026 under the LTIP's dividend reinvestment feature.

On April 29, 2026, the reporting person's phantom stock units were settled for 9 shares of Community Financial System, Inc. common stock, and .4418 shares were settled in cash at the price of $63.17 per share.

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.

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.

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 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.

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 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.

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.

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.

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 ("DCP for Directors") will be settled in Community Financial System, Inc. common stock at future dates selected by the reporting person.

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 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.

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 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.

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.

Each restricted stock unit represents a contingent right to receive one share of Community Financial System, Inc. common stock.

The restricted stock units vest in three equal installments beginning March 1, 2027.

The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended ("LTIP"). Each phantom stock unit which represents a deferred stock unit is the economic equivalent of one share of Community Bank System, Inc. common stock and will be settled in common stock at a predetermined date.

Includes 9.6079 units of phantom stock acquired on January 12, 2026 under the LTIP's dividend reinvestment feature.

The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan"). 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 35.9672, 40.8617, 45.1866, and 41.4544 units of phantom stock acquired on April 10, 2025, July 10, 2025, October 10, 2025, and January 12, 2026, respectively, as dividend equivalents under the Plan.

The option vests ratably on March 17, 2027, 2028, 2029, 2030, and 2031.

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 55.1073 units of phantom stock acquired on January 12, 2026 under the LTIP's dividend reinvestment feature.

The option vests ratably on March 17, 2027, 2028, 2029, 2030, and 2031.

The option vests ratably on March 17, 2027, 2028, 2029, 2030, and 2031.

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 9.4706, 10.4729, and 9.6079 units of phantom stock acquired as dividend equivalents on July 10, 2025, October 10, 2025, and January 12, 2026, respectively, under the LTIP.

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.

The reporting person has received deferred stock units under the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan"). 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 20.9266 units of phantom stock acquired on January 12, 2026 under the Plan's dividend reinvestment feature.

The option vests ratably on March 17, 2027, 2028, 2029, 2030, and 2031.

Each restricted stock unit represents a contingent right to receive one share of Community Financial System, Inc. common stock.

The restricted stock units vest in three equal annual installments beginning March 1, 2027.

Each restricted stock unit represents a contingent right to receive on share of Community Financial System, Inc. common stock.

The restricted stock units vest in three equal installments beginning March 1, 2027.

The reporting person has received deferred stock units under the Community Bank System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan"). Each phantom stock unit which represents a deferred stock unit is the economic equivalent of one share of Community Bank System, Inc. common stock and will be settled in common stock at a predetermined date.

Includes 44.5994, 48.3956, 53.5179, and 49.0975 units of phantom stock acquired as dividend equivalents on April 10, 2025, July 10, 2025, October 10, 2025, and January 12, 2026, respectively, under the LTIP.

The option vests ratably on March 17, 2027, 2028, 2029, 2030, and 2031.

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.

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 19.1578, 21.1856, and 19.4356 units of phantom stock acquired on July 10, 2025, October 10, 2025, and January 12, 2026 under the LTIP's dividend reinvestment feature.

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.