Alliant Energy Corporation and its subsidiary Interstate Power and Light Company filed a combined Form 8-K with the SEC on August 21, 2026, disclosing the pricing and expected closing of a $500 million public offering of senior debentures by Interstate Power and Light Company.

Key Highlights

  • Offering size: Interstate Power and Light Company agreed to sell $500 million aggregate principal amount of 5.100% Senior Debentures due 2031.
  • Underwriting Agreement date: The Underwriting Agreement was entered into on August 18, 2026, with Mizuho Securities USA LLC, PNC Capital Markets LLC, U.S. Bancorp Investments, Inc., and Wells Fargo Securities, LLC as representatives.
  • Expected closing: The offering was expected to close on August 21, 2026, subject to standard closing conditions.
  • Indenture: The Debentures are to be issued under an Indenture dated August 20, 2003, between IPL and The Bank of New York Mellon Trust Company, N.A., as successor trustee.
  • Registration: The Debentures are registered pursuant to an automatic shelf registration statement on Form S-3 (Registration No. 333-276062-01), originally filed December 15, 2023.
  • Legal opinions: Ashurst Perkins Coie US LLP and Simmons Perrine PLC each issued opinions dated August 21, 2026, regarding legality and Iowa law matters, respectively.

Interstate Power and Light Company Prices $500M Debt Offering at 5.100%

According to the filing, Interstate Power and Light Company ("IPL"), a subsidiary of Alliant Energy Corporation (NASDAQ:LNT), entered into an Underwriting Agreement on August 18, 2026, with four representative underwriters: Mizuho Securities USA LLC, PNC Capital Markets LLC, U.S. Bancorp Investments, Inc., and Wells Fargo Securities, LLC. Under that agreement, IPL agreed to sell, and the Underwriters agreed to purchase, $500 million aggregate principal amount of IPL's 5.100% Senior Debentures due 2031 in a public offering.

The filing states that 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, and pursuant to an Officer's Certificate dated August 21, 2026, setting forth the terms of the Debentures. The offering is registered under the Securities Act of 1933, as amended, through an automatic shelf registration statement on Form S-3 (Registration No. 333-276062-01) that IPL filed with the SEC on December 15, 2023, supplemented by a Prospectus Supplement filed on August 18, 2026.

The 8-K was filed, according to the registrants, for the purpose of filing exhibits to the Registration Statement, including the Underwriting Agreement (Exhibit 1.1), the Officer's Certificate (Exhibit 4.1), and legal opinions from Ashurst Perkins Coie US LLP (Exhibit 5.1) and Simmons Perrine PLC (Exhibit 5.2). A press release announcing the pricing of the offering, dated August 18, 2026, was also filed as Exhibit 99.1. The report was signed by Robert J. Durian, Executive Vice President and Chief Financial Officer, on behalf of both Alliant Energy Corporation and Interstate Power and Light Company.

What Was Disclosed

The combined 8-K discloses that IPL priced a $500 million offering of 5.100% Senior Debentures due 2031 on August 18, 2026, with closing expected August 21, 2026, and files associated transaction documents and legal opinions as exhibits.