Third Coast Bancshares Inc美股招股说明书(2025-12-19版)

Proxy Statement and Prospectus of Third CoastBancshares, Inc. Proxy Statement of Keystone Bancshares, Inc. PROPOSED MERGER—YOUR VOTE IS VERY IMPORTANT To the Shareholders of Third Coast Bancshares, Inc. and Keystone Bancshares, Inc.: On October22, 2025, Third Coast Bancshares, Inc., a Texas corporation (“Third Coast”), Arch Merger Sub, Inc., a Texas corporation and whollyowned subsidiary of Third Coast (“Merger Sub”), and Keystone Bancshares, Inc., a Texas corporation (“Keystone”), entered into an Agreement and Planof Reorganization (the “merger agreement”). Subject to the terms and conditions of the merger agreement, Merger Sub will merge with and intoKeystone (the “merger”), with Keystone surviving as a wholly owned subsidiary of Third Coast. Immediately following, and in connection with, themerger, Third Coast will cause Keystone to be merged with and into Third Coast, with Third Coast surviving the merger (the “second merger”). At the effective time of the merger (the “effective time”), each outstanding share of common stock, par value $1.00 per share, of Keystone(“Keystone common stock”) will be converted into the right to receive, without interest, 0.45925 shares (the “exchange ratio”) of common stock, parvalue $1.00 per share, of Third Coast (“Third Coast common stock,” and such shares of Third Coast common stock, the “Stock Consideration”).However, the holder of each share of Keystone common stock will be entitled to elect to receive, without interest, an amount of cash equal to theproduct of (i)the exchange ratio, multiplied by (ii)the volume-weighted average price per share of Third Coast common stock for a 20 trading dayperiod, starting with the opening of trading on the 21st trading day prior to the calculation date (as defined below) to the closing of trading on the dayprior to the calculation date, rounded to the nearest cent, as reported by Bloomberg Finance L.P. (such volume-weighted average price per share, the“TCBX Closing VWAP,” and such amount of cash, the “Cash Election Consideration”), in lieu of such Stock Consideration in exchange for each of suchholder’s shares of Keystone common stock, provided that the aggregate Cash Election Consideration to be paid by Third Coast will not exceed$20,000,000. In the event that Keystone shareholders elect to receive aggregate Cash Election Consideration in an amount greater than $20,000,000, thedistribution of the aggregate Cash Election Consideration will be prorated among such shareholders in accordance with the terms of the mergeragreement. The exchange ratio is subject to reduction in the event that Keystone does not deliver a minimum of $94,576,000 of the sum of Keystone’scapital, surplus and retained earnings accounts less all intangible assets, calculated as of the calculation date and in accordance with generally acceptedaccounting principles of the United States (“GAAP”) consistently applied (the “Keystone equity”), and adjusted to reflect the payment of or accrual forall Keystone Merger Costs (as defined in the merger agreement) on an after-tax basis to the extent deducible for tax purposes (the “Keystone adjustedequity”). The Third Coast common stock is listed on the New York Stock Exchange (the “NYSE”) and NYSE Texas under the symbol “TCBX.” Themarket value of the Stock Consideration and the value of the Cash Election Consideration will fluctuate with the market price of Third Coast commonstock; therefore, the market value of the Stock Consideration and the value of the Cash Election Consideration at the effective time will not be known atthe time the Keystone shareholders vote on the merger agreement. Based on (i)(A) the closing price of $39.28 for Third Coast common stock on theNYSE on October22, 2025, the last trading day before public announcement of the merger, the implied value of the Stock Consideration would beapproximately $18.04, and (B)the TCBX Closing VWAP calculated as though the calculation date was October23, 2025, the implied value of the CashElection Consideration would be approximately $17.63, (ii)(A) the closing price of $37.11 for Third Coast common stock on the NYSE onNovember21, 2025, the latest practicable trading day before the initial filing of this joint proxy statement/prospectus, the implied value of the StockConsideration would be approximately $17.04, and (B)the TCBX Closing VWAP calculated as though the calculation date was November22, 2025, theimplied value of the Cash Election Consideration would be approximately $17.05, and Table of Contents (iii)(A) the closing price of $39.97 for Third Coast common stock on the NYSE on December 12, 2025, the latest practicable trading day before theprinting of this joint proxy statement/prospectus, the implied value of the Stock Consideration would be approximately $18.36, and (B)the TCBXClosing VWAP calculated as though the calculation date was December 13, 2025, the implied value of the Cash Election Consideration would beapproximately $17.58. Each of the fo