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): April 1, 2025

BYLINE BANCORP, INC.

(Exact Name of Registrant as Specified in Its Charter)

Delaware

(State or Other Jurisdiction

of Incorporation)

(773) 244-7000

(Registrant’s Telephone Number, Including Area Code)

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 Instruction A.2. below):

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

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. ☐

On April 1, 2025, Byline Bancorp, Inc., a Delaware corporation (“Byline”), issued a press release announcing the completion of its previously announced merger with First Security Bancorp, Inc., a Delaware corporation (“First Security Bancorp”), and First Security Bancorp’s wholly owned bank subsidiary, First Security Trust and Savings Bank, an Illinois chartered bank. As a result of the transaction, effective April 1, 2025, First Security Trust and Savings Bank was merged with and into Byline Bank. The Transaction brings Byline’s total assets to approximately $9.8 billion, based on information as of December 31, 2024.

Under the terms of the Merger Agreement, each share of First Security Bancorp’s common stock was converted into the right to receive 2.3539 shares of Byline common stock. First Security Bancorp’s preferred shares were redeemed in cash immediately prior to closing with an aggregate value of approximately $2.4 million. The value of the total merger consideration at closing was approximately $41.5 million. A copy of the press release relating to the closing of the Transaction is furnished herewith as Exhibit 99.1 and incorporated herein by reference.

The information furnished pursuant to this Item 7.01 (including Exhibit 99.1 hereto) is being furnished and shall not be deemed “filed” under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing by Byline under the Securities Act of 1933, as amended, or the Exchange Act, except as may be expressly set forth by specific reference in such filing. The furnishing of information pursuant to this Item 7.01 will not be deemed an admission as to the materiality of any information in this Current Report on Form 8-K that is required to be disclosed solely by Regulation FD.

(d) Exhibits.

SIGNATURE

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