Sec Form 5 Filing - SCOTT JAMES R @ FIRST INTERSTATE BANCSYSTEM INC - 2025-12-31

FORM 5 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 SCOTT JAMES R 2. Issuer Name and Ticker or Trading Symbol FIRST INTERSTATE BANCSYSTEM INC [ FIBK] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) P.O. BOX 7113 3. Date of Earliest Transaction (MM/DD/YY) 12/31/2025 (Street) BILLINGS,, MT59103 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 2,531,970 ( 1 ) I See footnotes ( 1 ) ( 2 ) ( 3 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SCOTT JAMES R P.O. BOX 7113 BILLINGS,, MT59103 X James R Scott Trust, James R Scott & First Interstate Wealth Management Co-TTEEs P.O. BOX 7113 BILLINGS,, MT59103 X JS Investments Limited Partnership P.O. BOX 7113 BILLINGS,, MT59103 X James R & Christine M Scott Foundation P.O. BOX 7113 BILLINGS,, MT59103 X Foundation for Community Vitality P.O. BOX 7113 BILLINGS,, MT59103 X James F Heyneman Conservatorship, James Scott, Conservator P.O. BOX 7113 BILLINGS,, MT59103 X James F Heyneman Trust, James Scott & First Interstate Wealth Management Co-Trustees P.O. BOX 7113 BILLINGS,, MT59103 X Signatures JAMES R SCOTT, By: ++ 02/17/2026 Signature of Reporting Person Date James R Scott Trust, James R Scott & First Interstate Wealth Management Co-TTEEs, By:++ 02/17/2026 Signature of Reporting Person Date James R & Christine M Scott Foundation, By: ++ 02/17/2026 Signature of Reporting Person Date Foundation for Community Vitality, By: ++ 02/17/2026 Signature of Reporting Person Date James F Heyneman Conservatorship, James Scott, Conservator, By: ++ 02/17/2026 Signature of Reporting Person Date James F Heyneman Trust, James Scott & First Interstate Wealth Management Co-Trustees, By: ++ 02/17/2026 Signature of Reporting Person Date ++ /s/ Timothy Leuthold, Attorney-in-Fact for Reporting Person 02/17/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Composed of 1,989,882 shares held of record by James R Scott Trust, James R Scott & First Interstate Wealth Management Co-TTEEs, 14,534 shares held of record by James R Scott's 401(k) plan, 35,240 shares held of record by James R and Christine M Scott Foundation, 346,563 shares held of record by Foundation for Community Vitality, 73,002 shares held of record by James F Heyneman Conservatorship, James Scott, Conservator, 31,879 shares held of record by James F Heyneman Trust, James Scott & First Interstate Wealth Management Co-Trustees, and 40,870 shares held of record by James R. Scott's spouse. James R Scott ceased to have an indirect reportable beneficial ownership interest in the 1,901,036 shares held of record by JS Investments Limited Partnership upon his resignation in November 2025 as the Managing General Partner of such partnership. ( 2 )As a result of agreements entered into among the reporting persons, the issuer, and other stockholders of the issuer signatory thereto, the reporting persons may be deemed members of a group with the other signatories thereto and may be deemed to share beneficial ownership of the securities reported therein. Each of the reporting persons disclaims beneficial ownership of any such securities, except to the extent of his or its pecuniary interest therein. The reporting persons expect to file future Forms 4 or 5, if any, together with James R. Scott with the indication of direct or indirect ownership in Tables I and II being made from James R. Scott's perspective, unless expressly noted otherwise by footnote. ( 3 )As a result of the resignation described in footnote 1 hereto, JS Investments Limited Partnership no longer intends to file future Forms 4 or 5 with the other reporting persons identified in the form. The nature of beneficial ownership is described in detail by footnote for all reporting persons.

Remarks: Form filed solely to reflect that JS Investments Limited Partnership is no longer filing Forms 4 and 5 together with the other reporting persons herein.

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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