Third Coast Bancshares, Inc.

Third Coast Bancshares, Inc., a Texas corporation ("Third Coast"), and Great Plains Bancshares, Inc., an Oklahoma corporation ("Great Plains"), issued a joint press release on October 7, 2026 announcing the execution of the Merger Agreement (as defined below). A copy of the press release is furnished as Exhibit 99.1 and incorporated herein by reference. Third Coast also intends to provide supplemental information regarding the transactions disclosed under Item 8.01 of this Current Report on Form 8-K in connection with presentations to analysts and investors. The slides that will be made available in connection with the presentations are furnished as Exhibit 99.2 and are incorporated herein by reference. In connection with the announcement of the Merger Agreement, Third Coast sent a written communication to employees of Third Coast Bank, which is furnished as Exhibit 99.3 and incorporated herein by reference, and Great Plains sent a written communication to employees of Great Plains National Bank, which is furnished as Exhibit 99.4 and incorporated herein by reference. As provided in General Instruction B.2 to Form 8-K, the information furnished in Item 7.01 and Exhibits 99.1, 99.2, 99.3, and 99.4 of this Current Report on Form 8-K shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, and such information shall not be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the "Securities Act"), or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

On October 6, 2026, Third Coast entered into an Agreement and Plan of Reorganization (the "Merger Agreement"), by and among Third Coast, Thunder Merger Sub, Inc., a Texas corporation and a wholly owned subsidiary of Third Coast ("Merger Sub"), and Great Plains, pursuant to which, upon the terms and subject to the conditions set forth therein, (i) Merger Sub will merge with and into Great Plains (the "Merger"), with Great Plains surviving as a wholly owned subsidiary of Third Coast, (ii) immediately following, and in connection with, the Merger, Great Plains will be merged with and into Third Coast, with Third Coast surviving the merger (the "Second Step Merger"), and (iii) immediately following the Second Step Merger, or at such later time as Third Coast may determine, Great Plains National Bank, a national banking association and a wholly owned subsidiary of Great Plains, will merge with and into Third Coast Bank, a Texas banking association and a wholly owned subsidiary of Third Coast, with Third Coast Bank surviving the merger.

Item 9.01 Financial Statements and Exhibits.

99.1 Press Release dated October 7, 2026

99.2 Investor Presentation, dated October 7, 2026

99.3 Third Coast Email to Third Coast Bank Employees

99.4 Great Plains Email to Great Plains National Bank Employees

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No Offer or Solicitation This communication is being made in respect of the proposed merger transaction involving Third Coast and Great Plains. This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or the solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act and otherwise in accordance with applicable law. Important Additional Information and Where to Find It Third Coast intends to file a registration statement on Form S-4 with the SEC, which will include a joint proxy statement of Great Plains and Third Coast that also constitutes a prospectus of Third Coast, and Third Coast will file other documents regarding the proposed transaction with the SEC. A definitive joint proxy statement/prospectus will also be sent to Great Plains' and Third Coast's shareholders seeking the required shareholder approvals of the proposed transaction. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT ON FORM S-4 AND THE JOINT PROXY STATEMENT/PROSPECTUS INCLUDED WITHIN THE REGISTRATION STATEMENT ON FORM S-4 WHEN THEY BECOME AVAILABLE, AS WELL AS ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC IN CONNECTION WITH THE TRANSACTION OR INCORPORATED BY REFERENCE INTO THE REGISTRATION STATEMENT ON FORM S-4 AND THE JOINT PROXY STATEMENT/PROSPECTUS, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION REGARDING THIRD COAST, GREAT PLAINS, THE TRANSACTION AND RELATED MATTERS. The documents filed by Third Coast with the SEC may be obtained free of charge at the SEC's website at www.sec.gov. In addition, the documents filed by Third Coast may be obtained free of charge at its website at https://ir.thirdcoast.bank/financials/sec-filings/. Alternatively, these documents, when available, can be obtained free of charge from Third Coast upon written request to Third Coast Bancshares, Inc., Attn: Investor Relations, 1800 West Loop South, Suite 800, Houston, TX 77027, or by calling (713) 960-1300. Participants in this Transaction Third Coast, Great Plains, their respective directors and executive officers and certain of their other members of management and employees may be deemed to be participants in the solicitation of proxies from Great Plains' shareholders and Third Coast's shareholders in connection with the proposed transaction. Information about the directors and executive officers of Third Coast may be found in Third Coast's Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on March 4, 2026 and in Third Coast's proxy statement for its 2026 Annual Meeting of Shareholders, as filed with the SEC on April 16, 2026, copies of which can be obtained free of charge from Third Coast or from the SEC's website as indicated above. To the extent the holdings of Third Coast's securities by its directors and executive officers have changed since the amounts set forth in Third Coast's proxy statement for its 2026 Annual Meeting of Shareholders, such changes have been or will be reflected on Statements of Changes in Beneficial Ownership of Securities on Form 4 filed with the SEC. Additional information regarding the interests of these participants and other persons who may be deemed participants in the transaction will be included in the joint proxy statement/prospectus and other relevant materials when filed with the SEC.