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 27~~February 2, 2026

PROSPERITY BANCSHARES, INC.

(Exact name of registrant as specified in its charter)

     (State or other jurisdiction
of incorporation)

     (Commission
File Number)

     (IRS Employer
Identification No.)

    

4295 San Felipe

Houston, Texas 77027

(Address of principal executive offices including zip code)

Registrant’'s telephone number, including area code: (281) 269-7199

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):

☒☐ 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))

☐ 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		~~TradingSymbol~~Trading Symbol(s)		Name of each ~~exchangeon~~exchange on which registered
Common stock, par value $1.00 per share		PB		New York Stock Exchange, Inc.

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2).

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 18.01. ~~Entry~~Other ~~into a Material Definitive Agreement~~Events.

~~Merger~~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 banking association and a wholly-owned subsidiary of Southwest, merged with and into Prosperity Bank, a Texas banking association and a wholly-owned subsidiary of Prosperity, with Prosperity Bank continuing as the surviving bank. 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.

OnItem ~~January 27, 2026, Prosperity Bancshares, Inc~~9.,01 aFinancial ~~Texas~~Statements ~~corporation (“Prosperity”), entered into an Agreement~~ and ~~Plan of Merger (the “Merger Agreement”) with Stellar Bancorp, Inc~~Exhibits., 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 the Merger (the “Surviving Corporation”). Immediately following the Merger, Stellar’s wholly owned banking subsidiary, Stellar Bank, will merge with and into Prosperity’s wholly owned banking subsidiary, Prosperity Bank (the “Bank Merger”), which will continue as the surviving bank in the Bank Merger. The Merger Agreement was unanimously approved by the Board of Directors of each of Prosperity and Stellar.

(d)

~~Upon the terms and subject to the conditions set forth in the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each share of common stock, par value $0~~Exhibits.01 per share, of Stellar (“Stellar Common Stock”) outstanding immediately prior to the Effective Time, other than certain shares held by Prosperity or Stellar and shares held by a holder of Stellar Common Stock who has properly exercised applicable dissenters’ rights in respect of such share, will be converted into the right to receive (i) 0.3803 shares of common stock (the “Exchange Ratio”), par value $1.00 per share, of Prosperity (“Prosperity Common Stock”) and (ii) an amount in cash equal to $11.36 (the “Per Share Cash Merger Consideration”) ((i) and (ii) together, the “Per Share Merger Consideration”). Holders of Stellar Common Stock will receive cash in lieu of fractional shares.

At the Effective Time, each outstanding Stellar equity award will be treated as follows:


Exhibit Number		Description of Exhibit
99.1		Press Release issued by Prosperity Bancshares, Inc. dated February 2, 2026.
104		Cover Page Interactive Data File (embedded within the Inline XBRL document).

• Stellar Stock Options: Each Stellar stock option with a per-share exercise price that is less than the Per Share Merger Consideration Value will be cancelled and the holder of such cancelled option will be entitled to receive (without interest) an amount in cash equal to the product of (i) the excess of the Per Share Merger Consideration Value over the option’s per-share exercise price, multiplied by (ii) the number of shares of Stellar Common Stock subject to such stock option immediately prior to the Effective Time. Any Stellar stock option with a per-share exercise price that is equal to or greater than the Per Share Merger Consideration Value will be cancelled for no consideration. “Per Share Merger Consideration Value” refers to the sum of (1) the Per Share Cash Consideration plus (2) the product of (x) the Exchange Ratio multiplied by (y) the average of the closing sale prices of Prosperity Common Stock on the New York Stock Exchange as reported by The Wall Street Journal for the ten consecutive full trading days ending on and including the fifth trading day immediately preceding the closing date.

• Stellar Restricted Stock Awards. Each outstanding restricted stock award in respect of Stellar Common Stock subject solely to service-based vesting, repurchase or other lapse restriction will vest and be converted into the right to receive (without interest) the Per Share Merger Consideration.

• Stellar Performance Unit Awards. Each outstanding restricted unit award in respect of Stellar Common Stock subject to performance-based vesting will vest and be converted into the right to receive (without interest) a cash payment equal to the product of (a) the Per Share Merger Consideration Value multiplied by (b) the number of shares of Stellar Common Stock subject to such performance unit award, with achievement of applicable performance metrics determined to be equal to 100% of the target level (or, in the case of the performance units granted in 2024, 200% of the target level).

The Merger Agreement also provides that Prosperity will take all necessary corporate action so that, as of the Effective Time, the size of the Board of Directors of Prosperity (the “Prosperity Board”) and the Board of Directors of Prosperity Bank (the “Prosperity Bank Board”) will each be increased by two members. The Merger Agreement provides that, as of the Effective Time, two current directors of Stellar or Stellar Bank will be appointed to the Prosperity Board, and as of the effective time of the Bank Merger, two current directors of Stellar or Stellar Bank will be appointed to the Prosperity Bank Board (such individuals, the “Additional Directors”). Each of the Additional Directors will be designated by Stellar, subject to the approval of the Prosperity Board and the Prosperity Bank Board (not to be unreasonably withheld).

The Merger Agreement contains customary representations and warranties from both Prosperity and Stellar, and each party has agreed to customary covenants, including, among others, covenants relating to (1) the conduct of its business or the taking of certain extraordinary actions during the interim period between the execution of the Merger Agreement and the Effective Time and (2) Stellar’s obligation to call a meeting of its shareholders to approve the Merger and the Merger Agreement, and, subject to certain exceptions, to recommend that its shareholders approve the Merger and the Merger Agreement. Stellar has also agreed to certain non-solicitation obligations related to alternative business combination proposals.

The completion of the Merger is subject to customary conditions, including (1) approval of the Merger Agreement by Stellar’s shareholders, (2) authorization for listing on the New York Stock Exchange of the shares of Prosperity Common Stock to be issued in the Merger, subject to official notice of issuance, (3) the receipt of required regulatory approvals, including the approval or waiver of prior approval of the Board of Governors of the Federal Reserve System, the Federal Deposit Insurance Corporation and the Texas Department of Banking, (4) effectiveness of the registration statement on Form S-4 for the Prosperity Common Stock to be issued in the Merger, and (5) the absence of any order, injunction, decree or other legal restraint preventing the completion of the Merger, the Bank Merger or any of the other transactions contemplated by the Merger Agreement or making the completion of the Merger, the Bank Merger or any of the other transactions contemplated by the Merger Agreement illegal. Each party’s obligation to complete the Merger is also subject to certain additional customary conditions, including (i) subject to certain exceptions, the accuracy of the representations and warranties of the other party, (ii) performance in all material respects by the other party of its obligations under the Merger Agreement and (iii) receipt by such party of an opinion from counsel to the effect that the Merger will qualify as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended.

The Merger Agreement provides certain termination rights for both Prosperity and Stellar and further provides that a termination fee of $78 million will be payable by Stellar upon termination of the Merger Agreement under certain circumstances.

The foregoing description of the Merger Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Merger Agreement, which is attached hereto as Exhibit 2.1 and is incorporated herein by reference.

The representations, warranties and covenants of each party set forth in the Merger Agreement have been made only for the purposes of, and were and are solely for the benefit of the parties to, the Merger Agreement, may be subject to limitations agreed upon by the contracting parties, including being qualified by confidential disclosures made for the purposes of allocating contractual risk between the parties to the Merger Agreement instead of establishing these matters as facts, and may be subject to standards of materiality applicable to the parties that differ from those applicable to investors. Accordingly, the representations and warranties may not describe the actual state of affairs at the date they were made or at any other time, and investors should not rely on them as statements of fact. In addition, such representations and warranties (1) will not survive consummation of the Merger, and (2) were made only as of the date of the Merger Agreement or such other date as is specified in the Merger Agreement. Moreover, information concerning the subject matter of the representations and warranties may change after the date of the Merger Agreement, which subsequent information may or may not be fully reflected in the parties’ public disclosures. Accordingly, the Merger Agreement is included with this filing only to provide investors with information regarding the terms of the Merger Agreement, and not to provide investors with any factual information regarding Prosperity or Stellar, their respective affiliates or their respective businesses. The Merger Agreement should not be read alone, but should instead be read in conjunction with the other information regarding Prosperity, Stellar, their respective affiliates or their respective businesses, the Merger Agreement and the Merger that will be contained in, or incorporated by reference into, the registration statement on Form S-4 to be filed by Prosperity that will include a proxy statement of Stellar and also constitute a prospectus of Prosperity, as well as in the Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and other filings that each of Prosperity and Stellar make with the Securities and Exchange Commission (the “SEC”).

Voting Agreements

Concurrently with the execution and delivery of the Merger Agreement, Prosperity entered into a voting agreement (each, a “Voting Agreement”) with each member of the Board of Directors of Stellar, who collectively hold the power to vote approximately 8.8% of the issued and outstanding Stellar Common Stock. Pursuant to the Voting Agreement, each such director has agreed, among other things and subject to the terms of the Voting Agreement, to (a) vote the shares of Stellar Common Stock of which he or she holds and has the power to vote or direct the voting (the “Subject Shares”) in favor of the approval of the Merger Agreement and (b) not transfer his or her Subject Shares, with certain limited exceptions. Each Voting Agreement will terminate upon the earlier of (i) termination of the Merger Agreement or (ii) the Effective Time.

The foregoing description of the Voting Agreements does not purport to be complete and is qualified in its entirety by reference to the full text of the Voting Agreements, the form of which is attached hereto as Exhibit 10.1 and incorporated by reference herein.

Director Support Agreements

Concurrently with the execution and delivery of the Merger Agreement, Prosperity entered into a director support agreement (each, a “Support Agreement”) with members of the Board of Directors of Stellar. Pursuant to the Support Agreement, each such director has agreed, among other things and subject to the terms of the Support Agreement and limited exceptions therein, for a period of two years after the date of the Effective Time, not to (i) disclose or use confidential information of Prosperity, Prosperity Bank, Stellar, Stellar Bank, or any of their respective subsidiaries and affiliates (each a “Covered Entity”), (ii) solicit customers of a Covered Entity or (iii) solicit certain employees of a Covered Entity.

The foregoing description of the Support Agreements does not purport to be complete and is qualified in its entirety by reference to the full text of the Support Agreements, the form of which is attached hereto as Exhibit 10.2 and incorporated by reference herein.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description of Exhibit
2.1		Agreement and Plan of Merger, dated as of January 27, 2026, by and between Prosperity Bancshares, Inc. and Stellar Bancorp, Inc.*
10.1		Form of Voting Agreement, dated as of January 27, 2026, by and between Prosperity Bancshares, Inc. and each director of Stellar Bancorp, Inc.
10.2		Form of Director Support Agreement, dated as of January 27, 2026, by and among Prosperity Bancshares, Inc., Prosperity Bank, Stellar Bancorp, Inc., Stellar Bank, and directors of Stellar Bancorp, Inc.
104		Cover Page Interactive Data File - the cover page XBRL tags are embedded within the Inline XBRL document.

* Pursuant to Item 601(a)(5) of Regulation S-K, certain schedules and similar attachments have been omitted. The registrant hereby agrees to furnish a copy of any omitted schedule or similar attachment to the SEC upon request.

Cautionary Notes on Forward Looking Statements

This Current Report on Form 8-K contains statements regarding the proposed transaction between Prosperity Bancshares, Inc. (“Prosperity”) and Stellar Bancorp, Inc. (“Stellar”); future financial and operating results; benefits

and synergies of the proposed transaction; future opportunities for Prosperity; the issuance of common stock of Prosperity contemplated by the Agreement and Plan of Merger by and between Prosperity and Stellar (the “Merger Agreement”); the expected filing by Prosperity with the Securities and Exchange Commission (the “SEC”) of a registration statement on Form S-4 (the “Registration Statement”) and a prospectus of Prosperity and a proxy statement of Stellar to be included therein (the “Proxy Statement/Prospectus”); the expected timing of the closing of the proposed transaction; the ability of the parties to complete the proposed transaction considering the various closing conditions and any other statements about future expectations that constitute forward-looking statements within the meaning of the federal securities laws, including the meaning of the Private Securities Litigation Reform Act of 1995, as amended, Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended. From time to time, oral or written forward-looking statements may also be included in other information released to the public. Such forward-looking statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may,” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. Forward-looking statements include all statements other than statements of historical fact, including forecasts or trends, and are based on current expectations, assumptions, estimates, and projections about Prosperity, Stellar and their respective subsidiaries or related to the proposed transaction between Prosperity and Stellar and are subject to significant risks and uncertainties that could cause actual results to differ materially from the results expressed in such statements.

These forward-looking statements may include information about Prosperity’s and Stellar’s possible or assumed future economic performance or future results of operations, including future revenues, income, expenses, provision for loan losses, provision for taxes, effective tax rate, earnings per share and cash flows and Prosperity’s and Stellar’s future capital expenditures and dividends, future financial condition and changes therein, including changes in Prosperity’s and Stellar’s loan portfolio and allowance for loan losses, future capital structure or changes therein, as well as the plans and objectives of management for Prosperity’s and Stellar’s future operations, future or proposed acquisitions, the future or expected effect of acquisitions on Prosperity’s and Stellar’s operations, results of operations, financial condition, and future economic performance, statements about the anticipated benefits of the proposed transaction, and statements about the assumptions underlying any such statement.

These forward-looking statements are not guarantees of future performance and are based on expectations and assumptions Prosperity and Stellar currently believe to be valid. Because forward-looking statements relate to future results and occurrences, many of which are outside of the control of Prosperity and Stellar, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict. Many possible events or factors could adversely affect the future financial results and performance of Prosperity, Stellar or the combined company and could cause those results or performance to differ materially from those expressed in or implied by the forward-looking statements. Such risks and uncertainties include, among others: (1) the risk that the cost savings and synergies from the proposed transaction may not be fully realized or may take longer than anticipated to be realized, (2) disruption to Prosperity’s and Stellar’s businesses as a result of the announcements and pendency of the proposed transaction, (3) the risk that the integration of Stellar’s businesses and operations into Prosperity will be materially delayed or will be more costly or difficult than expected, or that Prosperity is otherwise unable to successfully integrate Stellar’s business into its own, including as a result of unexpected factors or events, (4) the failure to obtain the necessary approval by the shareholders of Stellar, (5) the ability by Prosperity and/or Stellar to obtain required governmental approvals of the proposed transaction on the timeline expected, or at all, and the risk that such approvals may result in the imposition of conditions that could adversely affect Prosperity after the closing of the proposed transaction or adversely affect the expected benefits of the proposed transaction, (6) reputational risk and the reaction of each company’s customers, suppliers, employees or other business partners to the proposed transaction, (7) the failure of the closing conditions in the Merger Agreement to be satisfied, or any unexpected delay in closing the proposed transaction or the occurrence of any event, change or other circumstances that could give rise to the termination of the Merger Agreement, (8) the dilution caused by the issuances of additional shares of Prosperity’s common stock in the proposed transaction, (9) the possibility that the proposed transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events, (10) the outcome of any legal or regulatory proceedings that may be currently pending or later instituted against Prosperity before or after the proposed transaction, or against Stellar, (11) diversion of management’s attention from ongoing business operations and (12) general competitive, economic, political and

market conditions and other factors that may affect future results of Prosperity and Stellar. Prosperity and Stellar disclaim any obligation to update such factors or to publicly announce the results of any revisions to any of the forward-looking statements included herein to reflect future events or developments. These and various other risks, uncertainties, assumptions, and factors are discussed in the Annual Reports on Form 10-K for the year ended December 31, 2024, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, filed by Prosperity or Stellar and in other filings made by Prosperity and Stellar with the SEC from time to time.

Additional Information about the Transaction and Where to Find It

Prosperity intends to file with the SEC the Registration Statement on Form S-4 to register the shares of Prosperity common stock to be issued to the shareholders of Stellar in connection with the proposed transaction. The Registration Statement will include the Proxy Statement/Prospectus which will be sent to the shareholders of Stellar in connection with the proposed transaction. This communication is not a substitute for the Registration Statement, the Proxy Statement/Prospectus or any other document that may be filed by Prosperity or Stellar with the SEC. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT, THE PROXY STATEMENT/PROSPECTUS AND ANY OTHER RELEVANT DOCUMENTS TO BE FILED WITH THE SEC IN CONNECTION WITH THE PROPOSED TRANSACTION OR INCORPORATED BY REFERENCE INTO THE PROXY/STATEMENT PROSPECTUS, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THESE DOCUMENTS, CAREFULLY AND IN THEIR ENTIRETY, BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders will be able to obtain the Registration Statement and the Proxy Statement/Prospectus (when available) and other documents that are filed with the SEC by Prosperity or Stellar, as applicable, free of charge from the SEC’s website at https://www.sec.gov or through the investor relations section of Prosperity’s website at https://www.prosperitybankusa.com/investor-relations/ or Stellar’s website at https://ir.stellar.bank.

Participants in the Solicitation

Prosperity, Stellar and certain of their directors and executive officers and other employees may be deemed to be participants in the solicitation of proxies from Stellar’s shareholders in connection with the proposed transaction. Information about the directors and executive officers of Prosperity and their ownership of Prosperity common stock is contained in the definitive proxy statement for Prosperity’s 2025 annual meeting of shareholders (the “Prosperity Annual Meeting Proxy Statement”), which was filed with the SEC on March 13, 2025, including under the headings “Item 1. Election of Directors,” “Corporate Governance,” “Executive Compensation and Other Matters,” “Item 3. Advisory Vote on Executive Compensation,” and “Beneficial Ownership of Common Stock by Management of the Company and Principal Shareholders.” Information about the directors and executive officers of Stellar and their ownership of Stellar common stock is contained in the definitive proxy statement for Stellar’s 2025 annual meeting of shareholders (the “Stellar Annual Meeting Proxy Statement”), which was filed with the SEC on April 10, 2025, including under the headings “Proposal 1: Election of Directors,” “Certain Corporate Governance Matters,” “Executive Compensation and Other Matters,” “Executive Compensation Payments and Awards,” “Proposal 4: Advisory Vote on the Compensation of the Company’s Named Executive Officers (“Say-on-Pay Resolution”),” and “Beneficial Ownership of the Company’s Common Stock by Management and Principal Shareholders of the Company.” Additional information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of the shareholders of Stellar in connection with the proposed transaction, including a description of their direct or indirect interests, by security holdings or otherwise, will be included in the Proxy Statement/Prospectus relating to the proposed transaction when it is filed with the SEC. To the extent holdings of securities by potential participants (or the identity of such participants) have changed since the information printed in the Prosperity Annual Meeting Proxy Statement or the Stellar Annual Meeting Proxy Statement, such information has been or will be reflected on Statements of Change in Ownership on Forms 3 and 4 filed with the SEC, as applicable. Free copies of the Proxy Statement/Prospectus relating to the proposed transaction and free copies of the other SEC filings to which reference is made in this paragraph may be obtained from the SEC’s website at https://www.sec.gov or through the investor relations section of Prosperity’s website at https://www.prosperitybankusa.com/investor-relations/ or Stellar’s website at https://ir.stellar.bank.

No Offer or Solicitation

This communication is for informational purposes only and is not intended to and does not constitute an offer to subscribe for, buy or sell, or the solicitation of an offer to subscribe for, buy or sell, or an invitation to subscribe for, buy or sell any securities or a solicitation of any vote or approval in any jurisdiction, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in which such offer, invitation, sale or solicitation 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.

SIGNATURES

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.

			PROSPERITY BANCSHARES, INC.
	PROSPERITY BANCSHARES, INC.(Registrant)
			(Registrant)
Dated: February 2, 2026	By:	/s/ Charlotte M. Rasche
Dated: January 29, 2026			By:	/s/ Charlotte M. Rasche
		Name: Charlotte M. Rasche
				Name: Charlotte M. Rasche
		Title: Executive Vice President and General Counsel
				Title: Executive Vice President and General Counsel

8 3

Filing Compare · PROSPERITY BANCSHARES INC