INTERSTATE POWER & LIGHT CO

Item 8.01 Other Events. On May 13, 2025, Interstate Power and Light Company (“IPL”), a subsidiary of Alliant Energy Corporation, entered into an Underwriting Agreement (the “Underwriting Agreement”) with BofA Securities, Inc., Mizuho Securities USA LLC, MUFG Securities Americas Inc., and Wells Fargo Securities, LLC, as representatives of the several underwriters listed therein (the “Underwriters”), pursuant to which IPL agreed to sell, and the Underwriters agreed to purchase, subject to the terms and conditions set forth therein, $600 million aggregate principal amount of IPL’s 5.600% Senior Debentures due 2035 (the “Debentures”), in a public offering (the “Offering”). The Debentures are to be issued under an Indenture dated as of August 20, 2003, between IPL and The Bank of New York Mellon Trust Company, N.A., as successor trustee (the “Indenture”), pursuant to an Officer’s Certificate provided pursuant to the Indenture setting forth the terms of the Debentures, dated as of May 19, 2025 (the “Certificate”). The Offering is expected to close, subject to standard closing conditions, on May 19, 2025. The Debentures are registered under the Securities Act of 1933, as amended, pursuant to an automatic shelf registration statement on Form S-3 (Registration No. 333-276062-01) that IPL filed with the Securities and Exchange Commission (the “SEC”) on December 15, 2023 (the “Registration Statement”). The Registration Statement was supplemented by a Prospectus Supplement setting forth the terms of the Debentures that IPL filed with the SEC on May 15, 2025. This Current Report on Form 8-K is being filed for the purpose of filing exhibits to the Registration Statement relating to the public offering of the Debentures, and all such exhibits are hereby incorporated into the Registration Statement by reference. The Underwriting Agreement is filed as Exhibit 1.1 and the Certificate is filed as Exhibit 4.1 to this Form 8-K. On May 13, 2025, IPL issued a press release announcing that it had priced the Offering. The press release is filed as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference. Perkins Coie LLP, counsel to IPL, has issued an opinion to IPL, dated May 19, 2025, regarding the legality of the Debentures upon issuance thereof, and Simmons Perrine Moyer Bergman PLC, Iowa counsel to IPL, has issued an opinion to IPL, dated May 19, 2025, regarding certain legal matters relating to Iowa law. The opinions are filed as Exhibit 5.1 and Exhibit 5.2, respectively, hereto.