西南资本美股招股说明书(2025-11-03版)

Supplement No.4, dated November 3, 2025toProspectus, dated October 29, 2024 andProspectus Supplement, dated October 30, 2024 This supplement amends, supplements or modifies certain information contained in the prospectus supplement, dated October 30, 2024 (the“ATM Prospectus Supplement”), and the accompanying prospectus, dated October 29, 2024 (the “Base Prospectus,” and together with theATM Prospectus Supplement and the documents deemed incorporated by reference in each, the “Prospectus”), which relate to the sale ofshares of common stock of Capital Southwest Corporation in an “at-the-market” offering (the “ATM Program”) pursuant to those certain (i)third amended and restated equity distribution agreements, each dated May 26, 2021 and as amended from time to time, with each ofJefferies LLC (“Jefferies”) and Raymond James & Associates, Inc. (“Raymond James”) and (ii) amended and restated equity distributionagreements, each dated May 26, 2021 and as amended from time to time, with each of Citizens JMP Securities, LLC (f/k/a JMP SecuritiesLLC) (“Citizens Capital Markets”) and B. Riley Securities, Inc. (“B. Riley” and, together with Jefferies, Raymond James and CitizensCapital Markets, the “Sales Agents”). The terms the “Company,” “CSWC,” “we,” “us,” and “our” refer to Capital Southwest Corporationand its subsidiaries, unless indicated otherwise. Capitalized terms used but not defined herein shall have the same meaning given them in theATM Prospectus Supplement. You should carefully read the entire Prospectus and this supplement before investing in our common stock. This supplement should be readin conjunction with the Prospectus.You should also carefully consider the information set forth under the sections entitled “Risk Factors”on page S-9 of the ATM Prospectus Supplement, page 10 of the Base Prospectus and in our Annual Report on Form 10-K for the fiscalyear ended March 31, 2025, which is incorporated by reference into the Prospectus, as well as in our subsequent filings with theSecurities and Exchange Commission that are incorporated into the Prospectus, before investing in our common stock. STATUS OF THE "AT-THE-MARKET" OFFERING From March 4, 2019 to September 30, 2025, we sold a total of 36,843,069 shares of our common stock under the ATM Program for grossproceeds of approximately $792.0 million and net proceeds of approximately $777.9 million, after deducting commissions to the SalesAgents on shares sold and offering expenses. As a result and as of the date hereof, up to approximately $208.0 million in aggregate amountof our common stock remains available for sale under the ATM Program. FEES AND EXPENSES The following table is intended to assist you in understanding the costs and expenses you will bear directly or indirectly. We cautionyou that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise,whenever there is a reference to fees or expenses paid by “you,” “us” or “CSWC,” or that “we” will pay fees or expenses, you will indirectlybear such fees or expenses as investors in us. Shareholder Transaction Expenses:Sales load (as a percentage of offering price) Annual Expenses (as a percentage of net assets attributable to common stock for the fiscal quarterended September 30, 2025): Operating expenses2.92%(4)Interest payments on borrowed funds6.96%(5)Income tax provision/(benefit)0.86%(6)Total annual expenses10.74% (1)Represents the Sales Agents’ commission with respect to the shares of common stock being sold in this offering. There is no guarantee that there will be anyadditional sales of our common stock pursuant to the Prospectus.(2)The percentage reflects estimated offering expenses for this offering of approximately $2,500,000, of which we have incurred $2,000,000 as of October 30, 2025, and assumes that we sell all $1.0 billion of shares of common stock available under the equity distribution agreements with the Sales Agents.(3)The expenses of administering our dividend reinvestment plan (“DRIP”) are included in operating expenses. The DRIP does not allow shareholders to sell shares through the DRIP. If a shareholder wishes to sell shares they would be required to select a broker of their choice and pay any fees or other costs associated with thesale. (4)Operating expenses in this table represent the estimated annual operating expenses of CSWC and its consolidated subsidiaries based on actual operating expenses forthe quarter ended September 30, 2025. We do not have an investment adviser and are internally managed by our executive officers under the supervision of ourboard of directors. As a result, we do not pay investment advisory fees, but instead we pay the operating costs associated with employing investment managementprofessionals including, without limitation, compensation expenses related to salaries, discretionary bonuses and restricted stock grants.(5)Interest payments on borrowed funds represents (a) ou