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For more information, please see the SEC’s Web Site Privacy and Security Policy. Thank you for your interest in the U.S. Securities and Exchange Commission.

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By using this site, you are agreeing to security monitoring and auditing. For security purposes, and to ensure that the public service remains available to users, this government computer system employs programs to monitor network traffic to identify unauthorized attempts to upload or change information or to otherwise cause damage, including attempts to deny service to users.

Unauthorized attempts to upload information and/or change information on any portion of this site are strictly prohibited and are subject to prosecution under the Computer Fraud and Abuse Act of 1986 and the National Information Infrastructure Protection Act of 1996 (see Title 18 U.S.C. §§ 1001 and 1030).

To ensure our website performs well for all users, the SEC monitors the frequency of requests for SEC.gov content to ensure automated searches do not impact the ability of others to access SEC.gov content. We reserve the right to block IP addresses that submit excessive requests. Current guidelines limit users to a total of no more than 10 requests per second, regardless of the number of machines used to submit requests.

If a user or application submits more than 10 requests per second, further requests from the IP address(es) may be limited for a brief period. Once the rate of requests has dropped below the threshold for 10 minutes, the user may resume accessing content on SEC.gov. This SEC practice is designed to limit excessive automated searches on SEC.gov and is not intended or expected to impact individuals browsing the SEC.gov website.

Note that this policy may change as the SEC manages SEC.gov to ensure that the website performs efficiently and remains available to all users.

Note: We do not offer technical support for developing or debugging scripted downloading processes.

Form 8-KFalse000085456000008545602026-01-212026-01-21iso4217:USDxbrli:sharesiso4217:USDxbrli:shares

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):  January 21, 2026

GREAT SOUTHERN BANCORP, INC.

(Exact name of registrant as specified in its charter)

Maryland0-1808243-1524856 (State or Other Jurisdiction of Incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 1451 East Battlefield Springfield, Missouri 65804 (Address of Principal Executive Offices) (Zip Code) (417) 887-4400 (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: ☐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 classTrading Symbol(s)Name of each exchange on which registered Common Stock, par value $0.01 per shareGSBCThe NASDAQ Stock Market LLC

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 January 21, 2026, Great Southern Bancorp, Inc. issued a press release reporting preliminary financial results for the three months ended December 31, 2025. A copy of the press release, including unaudited financial information released as a part thereof, is attached as Exhibit 99.1 to this Current Report on Form 8-K and incorporated herein by reference.

Item 7.01. Regulation FD Disclosure.

The Company also published an investor presentation and loan portfolio related to its fourth quarter 2025 financial results, which are available on its website. A copy of the investor presentations are attached as Exhibit 99.2 and Exhibit 99.3.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit Number Description

99.1 Press Release dated January 21, 2026 99.2 Earnings Presentation 99.3 Loan Portfolio 104 Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURE

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 hereunto duly authorized.

GREAT SOUTHERN BANCORP, INC.

Date: January 21, 2026By: /s/ Joseph W. Turner Joseph W. Turner President and Chief Executive Officer