Other Events. On August 18, 2026, Interstate Power and Light Company (“IPL”), a subsidiary of Alliant Energy Corporation, entered into an Underwriting Agreement (the “Underwriting Agreement”) with Mizuho Securities USA LLC, PNC Capital Markets LLC, U.S. Bancorp Investments, 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…

Results of Operations and Financial Condition. On July 30, 2026, Alliant Energy Corporation issued a press release announcing its financial results for the three and six months ended June 30, 2026. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Results of Operations and Financial Condition. On April 30, 2026, Alliant Energy Corporation issued a press release announcing its financial results for the three months ended March 31, 2026. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Entry into a Material Definitive Agreement. On March 19, 2026, Alliant Energy Corporation (the “Company”), entered into a distribution agreement (the “Distribution Agreement”) with Barclays Capital Inc., BofA Securities, Inc., Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC, KeyBanc Capital Markets Inc., Mizuho Securities USA LLC, MUFG Securities Americas Inc., TD Securities (USA) LLC, and Wells Fargo Securities, LLC, as agents (the “Agents” and each, an “Agent”), and Barclays Bank PLC, B…

Entry into a Material Definitive Agreement. On March 2, 2026, Alliant Energy Corporation (the “Company”) entered into a term loan credit agreement (the “Credit Agreement”) among the Company, U.S. Bank National Association, as Administrative Agent, and the several lenders party thereto. The Credit Agreement provides for a $400 million term loan facility. The Credit Agreement also provides for an incremental term loan facility of up to $100 million. No lender has any obligation to provide incre…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information included or incorporated by reference in

Results of Operations and Financial Condition. On February 19, 2026, Alliant Energy Corporation issued a press release announcing its financial results for the fourth quarter and year ended December 31, 2025. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Director — Manu Asthana: The filing discloses the appointment of a new director to the board, which is a routine governance event and not the departure of a senior executive.

President — David A. de Leon: The President is retiring after 39 years with a named internal successor (Rebecca Cameron Valcq) appointed to take over the role, indicating an orderly succession rather than a sudden loss of leadership.

Other Events. On December 2, 2025, Wisconsin Power and Light Company (“WPL”), a subsidiary of Alliant Energy Corporation, entered into an Underwriting Agreement (the “Underwriting Agreement”) with Mizuho Securities USA LLC, Wells Fargo Securities, LLC, BofA Securities, Inc. and MUFG Securities Americas Inc., as representatives of the several underwriters listed therein (the “Underwriters”), pursuant to which WPL agreed to sell, and the Underwriters agreed to purchase, subject to the terms and…

Results of Operations and Financial Condition. On November 6, 2025, Alliant Energy Corporation issued a press release announcing its financial results for the three and nine months ended September 30, 2025. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Other Events. On September 23, 2025, Alliant Energy Corporation (the “Company”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with BofA Securities, Inc., MUFG Securities Americas Inc., Barclays Capital Inc., Goldman Sachs & Co. LLC, and J.P. Morgan Securities LLC, as representatives of the several underwriters listed therein (the “Underwriters”), pursuant to which the Company agreed to sell, and the Underwriters agreed to purchase, subject to the terms and conditions s…

Other Events. On September 8, 2025, Interstate Power and Light Company (“IPL”), a subsidiary of Alliant Energy Corporation, entered into an Underwriting Agreement (the “Underwriting Agreement”) with KeyBanc Capital Markets Inc., PNC Capital Markets LLC, TD Securities (USA) LLC, and U.S. Bancorp Investments, Inc., 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 term…

Results of Operations and Financial Condition. On August 7, 2025, Alliant Energy Corporation issued a press release announcing its financial results for the three and six months ended June 30, 2025. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

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 c…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information included or incorporated by reference in

Entry into a Material Definitive Agreement. On May 15, 2025, Alliant Energy Corporation (the “ Company ”) completed its previously announced sale of $575 million aggregate principal amount of 3.250% Convertible Senior Notes due 2028 (the “ Notes ”), which amount includes the exercise in full of the $75 million option to purchase additional Notes granted to the initial purchasers, in a private offering to persons reasonably believed to be qualified institutional buyers pursuant to Rule 144A un…

of this Current Report on Form 8-K. The Notes were sold to the initial purchasers in reliance on the exemption from the registration requirements provided by Section 4(a)(2) of the Securities Act for resale to persons reasonably believed to be qualified institutional buyers as defined in, and in reliance on, Rule 144A of the Securities Act. The Notes and the underlying shares of Common Stock issuable upon conversion of the Notes, if any, have not been and will not be registered under the Secu…

Entry into a Material Definitive Agreement. On May 9, 2025, Alliant Energy Corporation (the “Company”), entered into a distribution agreement (the “Distribution Agreement”) with Barclays Capital Inc., BofA Securities, Inc., Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC, KeyBanc Capital Markets Inc., Mizuho Securities USA LLC, MUFG Securities Americas Inc., TD Securities (USA) LLC, and Wells Fargo Securities, LLC, as agents (the “Agents” and each, an “Agent”), and Barclays Bank PLC, Bank…

Results of Operations and Financial Condition. On May 8, 2025, Alliant Energy Corporation issued a press release announcing its financial results for the three months ended March 31, 2025. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Chairman of the Board — John O. Larsen: The Chairman of the Board is retiring with a pre-designated successor, representing an orderly succession rather than a sudden loss of leadership.

Entry into a Material Definitive Agreement. On March 3, 2025, Alliant Energy Finance, LLC (“AEF”), a wholly-owned subsidiary of Alliant Energy Corporation (“Alliant Energy”), entered into a one-year second amended and restated term loan credit agreement (the “Credit Agreement”) with U.S. Bank National Association, as administrative agent, and the several lenders party thereto. The initial principal amount available under the Credit Agreement is $300 million, with a maturity on March 2, 2026.…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information included or incorporated by reference in

Results of Operations and Financial Condition. On February 20, 2025, Alliant Energy Corporation issued a press release announcing its financial results for the fourth quarter and year ended December 31, 2024. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Chief Accounting Officer — Dylan Syse: The filing discloses the internal promotion of Dylan Syse to Chief Accounting Officer and Controller, with the incumbent moving to Treasurer, representing an orderly succession rather than a departure.