Form 8-K

8-K — FIRST INTERSTATE BANCSYSTEM INC

Accession: 0000860413-26-000048

Filed: 2026-05-29

Period: 2026-05-27

CIK: 0000860413

SIC: 6022 (STATE COMMERCIAL BANKS)

Item: Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers: Compensatory Arrangements of Certain Officers

Item: Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year

Item: Submission of Matters to a Vote of Security Holders

Item: Financial Statements and Exhibits

Documents

8-K — fibk-20260527.htm (Primary)

EX-3.1 (fibk-20260529xex31_certxof.htm)

XML — IDEA: XBRL DOCUMENT (R1.htm)

8-K

8-K (Primary)

Filename: fibk-20260527.htm · Sequence: 1

fibk-20260527

false000086041312/3100008604132026-05-272026-05-2700008604132026-12-312026-12-31

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): May 27, 2026

------------------------------

FIRST INTERSTATE BANCSYSTEM, INC.

(Exact name of registrant as specified in its charter)

------------------------------

Delaware 001-34653 81-0331430

(State or other jurisdiction of

incorporation or organization) (Commission

File No.) (IRS Employer

Identification No.)

401 North 31st Street

Billings,

59101

(Address of principal executive offices) (zip code)

(406) 255-5311

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

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 (see General Instruction A.2. below):

☐ Written communications 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 exchange on which registered

Common stock, $0.00001 par value FIBK NASDAQ

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 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

Pursuant to the director retirement policy set forth in the Corporate Governance Guidelines of First Interstate BancSystem, Inc. (the “Company”), on May 27, 2026, each of Ms. Patricia L. Moss and Messrs. David L. Jahnke and Stephen M. Lacy, each having reached the retirement age of 72, was deemed to have retired and resigned automatically from the Company’s Board of Directors (the “Board”) as a Class II, Class III and Class I director, respectively, effective immediately prior to the Company’s 2026 annual meeting of shareholders (the “2026 Annual Meeting”). None of the retirements was related to any disagreement with the Company on any matter relating to the Company’s operations, policies, or practices. The Company thanks Ms. Moss and Messrs. Jahnke and Lacy for their years of dedicated service and many contributions to the Company and wishes them each well in retirement.

In connection with the retirements described above, the Company reduced the size of the Board from 14 to 11 directors and correspondingly reduced the number of directors in each class of the Board to eliminate any vacancy that otherwise would have resulted from the retirements.

Item 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year.

As described in Item 5.07 below, at the 2026 Annual Meeting, the Company’s shareholders approved an amendment to the Company’s Certificate of Incorporation (the “Charter Amendment”) to implement in conjunction with the Company’s Amended and Restated Bylaws (the “Bylaws”) a plurality voting standard with respect to the election of directors in the event of a contested election of directors, as defined in the Bylaws. A majority vote standard will continue to apply for the election of directors in an uncontested election. On May 28, 2026, the Company filed the Charter Amendment with the Secretary of State of Delaware, at which time the Charter Amendment became effective.

The foregoing description of the Charter Amendment is qualified in its entirety by reference to, and should be read in conjunction with, the complete text of the Charter Amendment, a copy of which is filed as Exhibit 3.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Item 5.07 Submission of Matters to a Vote of Security Holders.

At the 2026 Annual Meeting held on May 27, 2026, the proposals voted upon and the final voting results for each proposal are as follows:

Proposal No. 1 - To elect as Class II directors the following nominees proposed by the Board to three-year terms expiring at the 2029 annual meeting of shareholders of the Company, or until their respective successors have been elected and qualified or until such person’s earlier death, resignation or removal.

Name of Nominee For Against Abstentions Broker Non-Votes

Alice S. Cho 69,585,766 948,445 3,491,502 5,725,652

Dennis L. Johnson 69,589,375 944,689 3,491,649 5,725,652

Daniel A. Rykhus 66,325,640 4,209,058 3,491,015 5,725,652

Proposal No. 2 - To approve the Charter Amendment.

For Against Abstentions Broker Non-Votes

72,701,511 1,281,015 43,187 5,725,652

Proposal No. 3 - To approve, on a non-binding, advisory basis, the compensation of the Company’s named executive officers.

For Against Abstentions Broker Non-Votes

68,855,208 5,062,682 107,823 5,725,652

Proposal No. 4 - To ratify the appointment of Ernst & Young LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2026.

For Against Abstentions Broker Non-Votes

79,488,279 233,150 29,936 —

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No. Exhibit Description

3.1

Certificate of Amendment to the Certificate of Incorporation of First Interstate BancSystem, Inc.

104 Cover Page Interactive Data File (embedded within Inline XBRL document).

SIGNATURES

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.

Date: May 29, 2026

FIRST INTERSTATE BANCSYSTEM, INC.

By: /s/ JAMES A. REUTER

James A. Reuter

President and Chief Executive Officer

EX-3.1

Filename: fibk-20260529xex31_certxof.htm · Sequence: 2

Document

Exhibit 3.1

CERTIFICATE OF AMENDMENT

TO THE CERTIFICATE OF INCORPORATION

FIRST INTERSTATE BANCSYSTEM, INC.

a Delaware corporation

Pursuant to Section 242 of the General Corporation Law of the State of Delaware (the “DGCL”), First Interstate BancSystem, Inc., a corporation organized and existing under the DGCL (the “Corporation”), hereby certifies as follows:

A.On February 24, 2026, the Board of Directors of the Corporation duly adopted resolutions setting forth and declaring advisable the following amendment (the “Amendment”) to the Corporation’s Certificate of Incorporation (the “Certificate”) and directing that the Amendment be submitted to the shareholders of the Corporation for approval at the Corporation’s 2026 Annual Meeting of Shareholders.

B.Section (d) of Article SEVENTH of the Certificate is hereby amended and restated in its entirety to read as follows:

“(d) Except as may otherwise be set forth in the Bylaws of the Corporation with respect to plurality voting in the event of a contested election (as such term is defined or used in the Bylaws) of directors, directors shall be elected by a majority of the voting power of the shares of capital stock present in person or represented by proxy at an annual meeting of shareholders and entitled to vote on the election of directors. There shall be no cumulative voting for directors of the Corporation.”

C.This Amendment to the Certificate has been duly adopted by the requisite vote of the shareholders of the Corporation at a meeting of shareholders duly called and held, in accordance with Section 242 of the DGCL.

D.This Amendment to the Certificate shall become effective upon filing with the Secretary of State of the State of Delaware.

IN WITNESS WHEREOF, the Corporation has caused this Certificate of Amendment to the Certificate of Incorporation to be signed by a duly authorized officer of the Corporation on this 28th day of May, 2026.

By: /s/ Kirk D. Jensen

Name: Kirk D. Jensen

Title: Executive Vice President and General Counsel

XML — IDEA: XBRL DOCUMENT

XML

Filename: R1.htm · Sequence: 7

v3.26.1

Cover

Dec. 31, 2026

May 27, 2026

Cover [Abstract]

Document Type

8-K

Document Period End Date

May 27, 2026

Entity Registrant Name

FIRST INTERSTATE BANCSYSTEM, INC.

Entity Incorporation, State or Country Code

Entity File Number

001-34653

Entity Tax Identification Number

81-0331430

Entity Address, Address Line One

401 North 31st Street

Entity Address, City or Town

Billings,

Entity Address, State or Province

Entity Address, Postal Zip Code

59101

City Area Code

(406)

Local Phone Number

255-5311

Written Communications

false

Soliciting Material

false

Pre-commencement Tender Offer

false

Pre-commencement Issuer Tender Offer

false

Title of 12(b) Security

Common stock, $0.00001 par value

Trading Symbol

FIBK

Security Exchange Name

NASDAQ

Amendment Flag

false

Entity Central Index Key

0000860413

Entity Emerging Growth Company

false

Current Fiscal Year End Date

--12-31

- Definition

Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.

+ References

No definition available.

+ Details

Name:

dei_AmendmentFlag

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Area code of city

+ References

No definition available.

+ Details

Name:

dei_CityAreaCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Cover page.

+ References

No definition available.

+ Details

Name:

dei_CoverAbstract

Namespace Prefix:

dei_

Data Type:

xbrli:stringItemType

Balance Type:

Period Type:

duration

- Definition

End date of current fiscal year in the format --MM-DD.

+ References

No definition available.

+ Details

Name:

dei_CurrentFiscalYearEndDate

Namespace Prefix:

dei_

Data Type:

xbrli:gMonthDayItemType

Balance Type:

Period Type:

duration

- Definition

For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

+ References

No definition available.

+ Details

Name:

dei_DocumentPeriodEndDate

Namespace Prefix:

dei_

Data Type:

xbrli:dateItemType

Balance Type:

Period Type:

duration

- Definition

The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

+ References

No definition available.

+ Details

Name:

dei_DocumentType

Namespace Prefix:

dei_

Data Type:

dei:submissionTypeItemType

Balance Type:

Period Type:

duration

- Definition

Address Line 1 such as Attn, Building Name, Street Name

+ References

No definition available.

+ Details

Name:

dei_EntityAddressAddressLine1

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the City or Town

+ References

No definition available.

+ Details

Name:

dei_EntityAddressCityOrTown

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Code for the postal or zip code

+ References

No definition available.

+ Details

Name:

dei_EntityAddressPostalZipCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the state or province.

+ References

No definition available.

+ Details

Name:

dei_EntityAddressStateOrProvince

Namespace Prefix:

dei_

Data Type:

dei:stateOrProvinceItemType

Balance Type:

Period Type:

duration

- Definition

A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityCentralIndexKey

Namespace Prefix:

dei_

Data Type:

dei:centralIndexKeyItemType

Balance Type:

Period Type:

duration

- Definition

Indicate if registrant meets the emerging growth company criteria.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityEmergingGrowthCompany

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.

+ References

No definition available.

+ Details

Name:

dei_EntityFileNumber

Namespace Prefix:

dei_

Data Type:

dei:fileNumberItemType

Balance Type:

Period Type:

duration

- Definition

Two-character EDGAR code representing the state or country of incorporation.

+ References

No definition available.

+ Details

Name:

dei_EntityIncorporationStateCountryCode

Namespace Prefix:

dei_

Data Type:

dei:edgarStateCountryItemType

Balance Type:

Period Type:

duration

- Definition

The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityRegistrantName

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityTaxIdentificationNumber

Namespace Prefix:

dei_

Data Type:

dei:employerIdItemType

Balance Type:

Period Type:

duration

- Definition

Local phone number for entity.

+ References

No definition available.

+ Details

Name:

dei_LocalPhoneNumber

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 13e

-Subsection 4c

+ Details

Name:

dei_PreCommencementIssuerTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14d

-Subsection 2b

+ Details

Name:

dei_PreCommencementTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Title of a 12(b) registered security.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b

+ Details

Name:

dei_Security12bTitle

Namespace Prefix:

dei_

Data Type:

dei:securityTitleItemType

Balance Type:

Period Type:

duration

- Definition

Name of the Exchange on which a security is registered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection d1-1

+ Details

Name:

dei_SecurityExchangeName

Namespace Prefix:

dei_

Data Type:

dei:edgarExchangeCodeItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14a

-Subsection 12

+ Details

Name:

dei_SolicitingMaterial

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Trading symbol of an instrument as listed on an exchange.

+ References

No definition available.

+ Details

Name:

dei_TradingSymbol

Namespace Prefix:

dei_

Data Type:

dei:tradingSymbolItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Securities Act

-Number 230

-Section 425

+ Details

Name:

dei_WrittenCommunications

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration