Columbia Financial, Inc./MD/

July 16, 2026 false 0002115119 0002115119 2026-06-23 2026-06-23 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): July 16, 2026 Columbia Financial, Inc. (Exact Name of Registrant as Specified in its Charter) Maryland 333-294103 42-1991301 (State or other jurisdiction (Commission (IRS Employer of incorporation) File Number) Identification Number) 19-01 Route 208 North , Fair Lawn , New Jersey 07410 (Address of principal executive offices) ( 800 ) 522-4167 (Registrant’s telephone number, including area code) 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: ☐ 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 Act: Title of each class Trading symbol(s) Name of each exchange on which registered None 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 8.01 Other Events On July 16, 2026, Columbia Financial, Inc., a Maryland corporation (the " Company "), issued a press release announcing the results of its firm commitment underwritten offering in connection with the second-step conversion of Columbia Financial, Inc., a Delaware corporation (the " Holding Company ", along with the final subscription offering exchange ratio with respect to shares of Holding Company common stock held by the Holding Company’s minority stockholders. The press release also announced the final merger exchange ratio in connection with the Company’s acquisition of Northfield Bancorp, Inc. The transactions are scheduled to close on July 20, 2026. A copy of the press release is filed as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference. Item 9.01 Financial Statements and Exhibits (d) Exhibits Exhibit Number Description 99.1 Press release dated July 16, 2026 104 Cover Page Interactive Data File (embedded within the Inline XBRL document) 2 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 hereunder duly authorized. Date: July 17, 2026 /s/Dennis E. Gibney Dennis E. Gibney 1 st Senior Executive Vice President, Chief Banking Officer 3