Sec Form 3 Filing - Doygun Eren @ GATX CORP - 2026-08-05

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Doygun Eren 2. Issuer Name and Ticker or Trading Symbol GATX CORP [ GATX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP Chief Plan. & Invest. Off. (Last) (First) (Middle) 233 S. WACKER DR. 3. Date of Earliest Transaction (MM/DD/YY) 08/05/2026 (Street) CHICAGO, IL60606 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 5,323 D Common Stock 401(k) 210 I 401(k)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares 2020 NQ Stock Option (Right to Buy) $ 77.07 01/31/2021( 1 ) 01/31/2027 Common Stock 1,000 D 2021 NQ Stock Option (Right to Buy) $ 91.36 01/29/2022( 1 ) 01/29/2028 Common Stock 1,600 D 2022 NQ Stock Option (Right to Buy) $ 103.15 01/28/2023( 1 ) 01/28/2029 Common Stock 1,500 D 2023 NQ Stock Option (Right to Buy) $ 113.28 01/26/2024( 1 ) 01/26/2030 Common Stock 1,300 D 2024 NQ Stock Option (Right to Buy) $ 126.468 01/25/2025( 1 ) 01/25/2031 Common Stock 1,300 D 2025 NQ Stock Option (Right to Buy) $ 166.193 01/30/2026( 1 ) 01/30/2032 Common Stock 1,300 D 2026 NQ Stock Option (Right to Buy) $ 196.4 02/23/2027( 1 ) 02/23/2033 Common Stock 2,400 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Doygun Eren 233 S. WACKER DR. CHICAGO, IL60606 SVP Chief Plan. & Invest. Off. Signatures Lisa Ibarra, by Power of Attorney on behalf of Eren Doygun 08/13/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )33.33% of Stock Option granted may be exercised commencing 1 year from the date of the grant, an additional 33.33% commencing 2 years from the date of the grant and the remaining 33.34% commencing 3 years from the date of the grant.

Remarks: Exhibit List: Exhibit 24 - Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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