Material Agreement · New Debt / Obligation

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): June 30, 2025     GATX Corporation (Exact name of registrant as specified in its charter)       New York   1-2328   36-1124040 (State or other jurisdiction of incorporation)   (Commission File Number)   (IRS Employer Identification No.) 233 South Wacker Drive Chicago , Illinois 60606 -7147 (Address of principal executive offices, including zip code) (312) 621-6200 (Registrant’s telephone number, including area code)     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:   ☐ Written communication 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)) Securities registered pursuant to Section 12(b) of the Act:   Title of Each Class   Trading Symbol(s)   Name of Each Exchange on Which Registered Common Stock   GATX   New York Stock Exchange     Chicago Stock Exchange Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). 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 1.01 Entry into a Material Definitive Agreement On June 30, 2025, GATX Corporation (the “Company”) entered into a Commitment Increase Supplement (the “Supplement”) among the Company, M&T Bank, as increasing lender (the “Increasing Lender”), PNC Bank, National Association, as issuing bank, U.S. Bank National Association, as issuing bank, and Citibank, N.A., as swing line bank and as administrative agent, to its existing Five Year Credit Agreement, dated as of May 21, 2024 (as amended, supplemented, or otherwise modified from time to time, the “Credit Agreement”), among the Company, Citibank, N.A. and BofA Securities, Inc., as joint lead arrangers and joint book managers, the lenders party thereto, and Citibank, N.A., as administrative agent. Pursuant to the Supplement, the Increasing Lender made a revolving credit commitment in an amount of $32 million to the Company. As a result of this increase, the aggregate revolving credit commitments of all lenders under the Credit Agreement increased from $600 million to $632 million. The foregoing description of the Supplement is a summary and is qualified in its entirety by reference to the full text of the Supplement, which is attached as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference.   Item 2.03 Creation of a Direct Financial Obligation or an Obligation Under an Off-Balance Sheet Arrangement of a Registrant. The information provided in Item 1.01 of this Current Report on Form 8-K is incorporated in this Item 2.03 by reference.   Item 9.01. Financial Statements and Exhibits. (d) Exhibits   Exhibit No.    Description 10.1    Commitment Increase Supplement, dated as of June 30, 2025, by and among GATX Corporation, M&T Bank as Increasing Lender, the additional parties thereto and Citibank, N.A., as Administrative Agent. 104    Cover Page Interactive Data File (embedded within the Inline XBRL document).   SIGNATURE 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.   GATX CORPORATION (Registrant) /s/ Thomas A. Ellman Thomas A. Ellman Executive Vice President and Chief Financial Officer Date: July 1, 2025