Employment Agreement with Jeff Lee

First Interstate BancSystem, Inc. and its subsidiary First Interstate Bank have executed an employment agreement with Mr. Jeff Lee, effective September 14, 2026. Mr. Lee is appointed Executive Vice President and Chief Operations Officer. The agreement details compensation, benefits, and terms of termination. If terminated without cause or for good reason, Mr. Lee is entitled to severance pay equivalent to one times his base salary plus one times his average annual cash incentive compensation over the preceding three years, payable over 12 months, along with 12 months of continued insurance coverage. In the event of termination within six months before or 18 months following a change in control, severance increases to two times base salary plus two times target annual cash incentive, with 24 months of continued insurance coverage. The agreement also includes 12-month non-competition and non-solicitation clauses, extending to 18 months if termination follows a change in control. Severance payments may be reduced to avoid excise taxes under Section 280G of the Internal Revenue Code if the net after-tax benefit would be greater without reduction.