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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

## FORM 8-K

##

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): September 30, 2025

Financial Institutions, Inc.

(Exact name of Registrant as Specified in Its Charter)

New York | 0-26481 | 16-0816610
(State or Other Jurisdiction of Incorporation) | (Commission File Number) | (IRS Employer Identification No.)
220 Liberty Street |
Warsaw, New York |  | 14569
(Address of Principal Executive Offices) |  | (Zip Code)

Registrant’s Telephone Number, Including Area Code: 585 786-1100

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instructions A.2. below):

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)
☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))
☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Securities Exchange Act of 1934:

Title of each class |  | Trading Symbol(s) |  | Name of each exchange on which registered
Common stock, par value $0.01 per share |  | FISI |  | Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

## Item 2.02 Results of Operations and Financial Condition.

On October 23, 2025, Financial Institutions, Inc. (the “Company”) issued a press release to report financial results for the third quarter ended September 30, 2025. The press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

## Item 7.01 Regulation FD Disclosure.

The Company published an investor presentation with data for the third quarter ended September 30, 2025. The presentation is available on the Company’s website at www.FISI-investors.com under “Events & Presentations”. Investors should note that the Company announces material information in Securities and Exchange Commission (“SEC”) filings and press releases. Based on guidance from the SEC, the Company may also use the Investor Relations section of its corporate website, www.FISI-investors.com, to communicate with investors about the Company. It is possible that the information posted there could be deemed to be material information. The information on the Company’s website is not incorporated by reference into this Current Report on Form 8-K.

This information is furnished pursuant to Item 7.01 of Form 8-K and shall not be deemed to be “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934 (“Exchange Act”), as amended, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, of the Exchange Act, whether made before or after the date of this report, except as shall be expressly set forth by specific reference in such filing.

## Item 9.01 Financial Statements and Exhibits.

d) Exhibits.

Exhibit Number |  | Description |  | Location
99.1 |  | Press Release issued by Financial Institutions, Inc. on October 23, 2025 |  | Filed Herewith
104 |  | Cover Page Interactive Data File (embedded within the Inline XBRL document) |  |

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

|  |  | Financial Institutions, Inc.
Date: | October 23, 2025 | By: | /s/ W. Jack Plants II
|  |  | W. Jack Plants II Executive Vice President, Chief Financial Officer and Treasurer