First Interstate BancSystem, Inc.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. Effective July 9, 2026, the employment of Mr. Kirk D. Jensen with the registrant and its wholly owned subsidiary First Interstate Bank as Executive Vice President and General Counsel/Corporate Secretary was terminated involuntarily and without cause under his employment agreement with the registrant and its subsidiary, a copy of which was filed as an exhibit to the registrant’s most recent annual report on Form 10-K filed with the Securities and Exchange Commission on February 26, 2026, and is incorporated herein by reference. The registrant expects to conduct a national search for a replacement for this role, which role is expected to be performed by the registrant’s other in-house lawyers until a successor is appointed. The employment termination is not the result of any disagreement with the registrant or its subsidiary over any of their financial reporting, operations, policies or practices, or any other matter. Cautionary Note Regarding Forward-Looking Statements Statements contained in this report constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These statements are predictive in nature and are identified by the use of the terms “expected,” “will,” “look forward to,” “aim,” and similar words or phrases indicating possible future expectations, events or actions. Statements concerning the registrant’s expectations concerning succession planning and legal team oversight are forward-looking statements. Such forward-looking statements are based on current expectations, assumptions and projections and are not guarantees of future performance or outcomes. These statements are subject to a number of known and unknown risks, uncertainties, and other factors, many of which are beyond the registrant’s ability to control or predict, which may cause actual events to be different materially from those expressed or implied herein. The registrant has provided additional information about the risks facing its business in its most recent annual report on Form 10-K, and any subsequent periodic and current reports on Forms 10-Q and 8-K, filed by it with the Securities and Exchange Commission. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date the statement was made and are expressly qualified in their entirety by the cautionary statements set forth herein and in the filings with the Securities and Exchange Commission identified above, which you should read in their entirety before making any investment or other decision with respect to our securities. We undertake no obligation to update or revise any forward-looking statements contained in this report, whether as a result of new information, future events or otherwise, except as otherwise required by applicable law.