and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Vice Chairman of Prosperity and Prosperity Bank — Robert R. Franklin, Jr.: Mr. Franklin was appointed as Vice Chairman of Prosperity and Prosperity Bank with significant compensation.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. In connection with the Transactions, on the Closing Date, Prosperity assumed Stellar’s obligations with respect to approximately $2.17 billion in obligations issued by the Federal Home Loan Bank of Dallas to Stellar Bank.

Completion of Acquisition or Disposition of Assets. Effective July 1, 2026 (the “Closing Date”), Prosperity Bancshares, Inc. (“Prosperity” or the “Company”) completed its previously announced acquisition of Stellar Bancorp, Inc., a Texas corporation (“Stellar”), pursuant to the Agreement and Plan of Merger, dated as of January 27, 2026 (the “Merger Agreement”), by and between Prosperity and Stellar. Pursuant to the Merger Agreement, Stellar merged with and into Prosperity (the “Merger”), with…

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Other Events. On February 2, 2026, Prosperity Bancshares, Inc. (“Prosperity”) issued a press release announcing the closing of the acquisition by Prosperity of Southwest Bancshares, Inc. (“Southwest”). Pursuant to the Agreement and Plan of Merger, dated as of September 30, 2025, by and between Prosperity and Southwest, Southwest merged with and into Prosperity, with Prosperity continuing as the surviving corporation (the “Merger”), and following the Merger, Texas Partners Bank, a Texas bankin…

Entry into a Material Definitive Agreement. Merger Agreement On January 27, 2026, Prosperity Bancshares, Inc., a Texas corporation (“Prosperity”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Stellar Bancorp, Inc., a Texas corporation (“Stellar”). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, Stellar will merge with and into Prosperity (the “Merger”), with Prosperity continuing as the surviving corporation in…

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Other Events. On January 2, 2026, Prosperity Bancshares, Inc. (“Prosperity”) issued a press release announcing the closing of the acquisition by Prosperity of American Bank Holding Corporation (“American”). Pursuant to the Agreement and Plan of Merger, dated as of July 17, 2025, by and between Prosperity and American, American merged with and into Prosperity, with Prosperity continuing as the surviving corporation (the “Merger”), and following the Merger, American Bank, National Association,…

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Other Events. Acquisition of Southwest Bancshares, Inc. On October 1, 2025, Prosperity issued a press release announcing that it had entered into a definitive merger agreement (the “Merger Agreement”) with Southwest Bancshares, Inc. (“Southwest”), a Texas corporation and bank holding company of Texas Partners Bank, a Texas banking association, pursuant to the terms and subject to conditions of which, Southwest will merge with and into Prosperity. On the terms and subject to the conditions of…

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Other Events. Acquisition of American Bank Holding Corporation On July 18, 2025, Prosperity issued a press release announcing that it had entered into a definitive merger agreement (the “Merger Agreement”) with American Bank Holding Corporation (“American”), a Texas corporation and bank holding company of American Bank, National Association, a national banking association, pursuant to the terms and subject to conditions of which, American will merge with and into Prosperity. On the terms and…

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

President and Chief Operating Officer — Kevin J. Hanigan: The filing discloses the execution of a new employment and change in control agreement for a sitting executive, which is a compensatory arrangement rather than a departure or change in personnel.

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Chairman and Chief Operating Officer — H.E. Timanus, Jr.: The filing discloses an amendment to an existing employment agreement regarding change-in-control benefits, not a departure, appointment, or election of an officer.

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

CEO — David Zalman: The filing discloses an amendment to an existing employment agreement regarding change-in-control severance terms, not an actual departure, appointment, or election of an officer.

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

and Exhibit 99.1 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, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Other Events. On April 1, 2024, Prosperity Bancshares, Inc. (“Prosperity”) issued a press release announcing the closing of the acquisition by Prosperity of Lone Star State Bancshares, Inc. A copy of Prosperity's press release is attached hereto as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.