Vanguard reports 5.46% stake in First Interstate BancSystem (NASDAQ: FIBK)

Rhea-AI Filing Summary

First Interstate BancSystem Inc ownership filing shows Vanguard Portfolio Management beneficially owns 5,523,702 shares of Common Stock, representing 5.46% of the class as of 03/31/2026. The filing reports sole voting power of 33,164 shares and sole dispositive power over 5,523,702 shares.

The Schedule 13G statement lists Vanguard Portfolio Management and affiliated divisions that exercise dispositive power over funds and managed accounts; the disclosure notes these holdings include securities held by Vanguard funds and managed clients.

Insights

Institutional Ownership Analyst

Vanguard's 5.46% stake is a standard institutional disclosure reflecting passive beneficial ownership.

The filing records 5,523,702 shares and a 5.46% ownership stake as of 03/31/2026. This is presented under Schedule 13G conventions for large passive holders rather than active activist positions.

Investor implications depend on Vanguard’s voting posture and fund-level trading; subsequent filings or amendments would show changes. The filing itself does not indicate planned transactions or changes to board or strategy.

SEC Filings / Compliance Specialist

Schedule 13G disclosure correctly itemizes voting and dispositive powers and cites SEC Release 34-39538.

The statement differentiates sole voting power (33,164) from sole dispositive power (5,523,702) and identifies affiliated entities exercising dispositive authority. The signature block is dated 04/29/2026.

File watchers should note this is a passive ownership disclosure; any shift to active intent would require Schedule 13D amendments and different disclosure thresholds.

Key Figures

Beneficial ownership: 5,523,702 shares Percent of class: 5.46% Sole voting power: 33,164 shares +3 more

6 metrics

Beneficial ownership 5,523,702 shares Schedule 13G as of <date>03/31/2026</date>

Percent of class 5.46% Ownership percentage reported on Schedule 13G

Sole voting power 33,164 shares Number of shares with sole power to vote

Sole dispositive power 5,523,702 shares Number of shares with sole power to dispose

CUSIP 32055Y201 Identifier for First Interstate Common Stock

Signature date 04/29/2026 Filing signed by Head of Global Fund Administration

Key Terms

Schedule 13G, beneficially owned, dispositive power, sole voting power

4 terms

Schedule 13G regulatory

"The filing is a Schedule 13G statement of beneficial ownership"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

beneficially owned financial

"reflects the securities beneficially owned, or deemed to be beneficially owned"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

dispositive power regulatory

"sole power to dispose or to direct the disposition of: 5523702"

Dispositive power is the authority to decide the final outcome of an asset, legal claim, contract, or corporate action — in effect the power to dispose of or resolve something. For investors it matters because whoever holds that authority can determine who gets paid, who controls an asset or vote, and how risks and returns are allocated; think of it like holding the key that lets you lock in the winner or loser in a deal.

sole voting power regulatory

"Sole Voting Power 33,164.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

First Interstate BancSystem Inc

(Name of Issuer)

Common Stock

(Title of Class of Securities)

32055Y201

(CUSIP Number)

03/31/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 32055Y201

1

Names of Reporting Persons

Vanguard Portfolio Management

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

PENNSYLVANIA

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 33,164.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 5,523,702.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

5,523,702.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

5.46 %

12

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person: In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by Vanguard Portfolio Management LLC and the following affiliates of Vanguard Portfolio Management LLC or business divisions of such affiliates: Vanguard Fiduciary Trust Company and Vanguard Global Advisers, LLC. This Schedule 13G includes securities held by Vanguard funds, or sleeves thereof, over which Vanguard Portfolio Management LLC exercises dispositive power, in addition to securities held by clients over which the affiliates or business divisions of such affiliates indicated above exercise dispositive and/or voting power. This Schedule 13G does not include securities, if any, beneficially owned by other subsidiaries or affiliates of Vanguard Portfolio Management LLC, or business divisions of such subsidiaries whose ownership of securities is disaggregated from that of the reporting business unit in accordance with such release.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: First Interstate BancSystem Inc
(b)	Address of issuer's principal executive offices: PO Box 30918, 401 North 31st Street, Billings, MT, 59107
Item 2.
(a)	Name of person filing: Vanguard Portfolio Management
(b)	Address or principal business office or, if none, residence: 100 Vanguard Blvd,, Malvern, PA, 19355
(c)	Citizenship: PA
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 32055Y201
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 5523702
(b)	Percent of class: 5.46 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 33164
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 5523702
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Vanguard Portfolio Management, including investment companies registered under the Investment Company Act of 1940 and other managed accounts, have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities reported herein.No one other person's interest in the securities reported herein is more than 5%.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Vanguard Portfolio Management

Signature:	Ashley Grim
Name/Title:	Head of Global Fund Administration
Date:	04/29/2026

FAQ

How many First Interstate (FIBK) shares does Vanguard own?

Vanguard Portfolio Management beneficially owns 5,523,702 shares of First Interstate Common Stock, per the Schedule 13G. The filing states this represents 5.46% of the class as of 03/31/2026.

What voting power does Vanguard report for FIBK?

Vanguard reports sole voting power over 33,164 shares. The filing also reports sole dispositive power over the full 5,523,702-share position as of 03/31/2026.

Is this Schedule 13G or 13D for First Interstate (FIBK)?

This is a Schedule 13G filing, which signals passive beneficial ownership. The filing lists Vanguard Portfolio Management and affiliated divisions exercising dispositive power over managed funds and accounts.

Does the filing say Vanguard will sell or buy more FIBK shares?

The Schedule 13G discloses current beneficial ownership only. It does not state any plans to buy or sell shares, nor does it describe trading intentions or future transactions.

Who signed the Schedule 13G for Vanguard?

The filing is signed by Ashley Grim, titled Head of Global Fund Administration, with signature date 04/29/2026, certifying the reported holdings.