A. Gillan Myer - 04 Mar 2026 Form 4 Insider Report for COMMUNITY FINANCIAL SYSTEM, INC. (CBU)

Role: EVP, Chief Admin & HR Officer
Signature: /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Maureen Gillan-Myer
Issuer symbol: CBU
Transactions as of: 04 Mar 2026
Net transactions value: $0
Form type: 4
Filing time: 06 Mar 2026, 13:50:58 UTC
Previous filing: 04 Mar 2026
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Gillan-Myer Maureen A	EVP, Chief Admin & HR Officer	C/O COMMUNITY FINANCIAL SYSTEM, INC., 333 BUTTERNUT DRIVE, SYRACUSE	/s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Maureen Gillan-Myer	06 Mar 2026	0001670754

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	CBU	Common Stock	Award		+2,562	+51%	$0.000000^*	7,590	04 Mar 2026	Direct	F1
transaction	CBU	Common Stock	Tax liability		-943	-12%	$59.87^*	6,647	04 Mar 2026	Direct	F2
holding	CBU	Common Stock						176	04 Mar 2026	By 401(k) Plan	F3

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	On March 4, 2026, the Compensation Committee approved the vesting of the three-year performance-based restricted stock award, granted to the reporting person in 2023, based on achievement of predetermined performance criteria at the target level. The reporting person received 2,304 shares of common stock under the award and 258.0628 shares of common stock acquired under the dividend reinvestment feature of the Community Financial System, Inc. 2022 Long-Term Incentive Plan, as amended (the "Plan").
F2	Payment of tax liability associated with vesting of restricted stock awards.
F3	The number of shares reported herein acquired pursuant to Community Financial System, Inc.'s 401(k) Plan and are based on a current plan statement.