X0508 4 2024-03-19 0000723188 COMMUNITY BANK SYSTEM, INC. CBU 0001242753 TRYNISKI MARK E C/O COMMUNITY BANK SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 0 Common Stock 59062 D Common Stock 98512 I By Phyllis Tryniski Family Trust Common Stock 27264 I By Mark Tryniski Family Trust Phantom Stock (Deferred Stock Units) 2024-03-19 4 A 0 1395 0 A Common Stock 1395 1395 D On March 6, 2024, the reporting person transferred 29,433 shares of common stock previously beneficially owned through the Community Bank System, Inc. 401(k) Employee Stock Ownership Plan. Includes 234 shares acquired pursuant to the Community Bank System, Inc. Dividend Reinvestment Plan. The reporting person is the trustee and his immediate family members are beneficiaries of the Phyllis Tryniski Family Trust. The reporting person disclaims beneficial ownership of the shares held by the trust, and this report should not be deemed an admission that the reporting person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose. The reporting person's spouse is the trustee of the Mark Tryniski Family Trust and his immediate family members are beneficiaries. The reporting person disclaims beneficial ownership of the shares held by the trust, and this report should not be deemed an admission that the reporting person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose. 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. Danielle M. Cima, pursuant to a Confirming Statement executed by Mark E. Tryniski 2024-03-21