Alliant Energy 10-Q 2026-06-30

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-Q

☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended June 30, 2026

or

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Name of Registrant, State of Incorporation, Address of Principal Executive Offices, Telephone Number, Commission File Number, IRS Employer Identification Number

ALLIANT ENERGY CORPORATION

(a Wisconsin Corporation)

4902 N. Biltmore Lane

Madison, Wisconsin 53718

Telephone (608) 458-3311

Commission File Number - 1-9894

IRS Employer Identification Number - 39-1380265

INTERSTATE POWER & LIGHT COMPANY

(an Iowa corporation)

Alliant Energy Tower

Cedar Rapids, Iowa 52401

Telephone (319) 786-4411

Commission File Number - 1-4117

IRS Employer Identification Number - 42-0331370

WISCONSIN POWER & LIGHT COMPANY

(a Wisconsin corporation)

4902 N. Biltmore Lane

Madison, Wisconsin 53718

Telephone (608) 458-3311

Commission File Number - 0-337

IRS Employer Identification Number - 39-0714890

This combined Form 10-Q is separately filed by Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company. Information contained in the Form 10-Q relating to Interstate Power and Light Company and Wisconsin Power and Light Company is filed by each such registrant on its own behalf. Each of Interstate Power and Light Company and Wisconsin Power and Light Company makes no representation as to information relating to registrants other than itself.

Securities registered pursuant to Section 12(b) of the Act:

Alliant Energy Corporation, Common Stock, $0.01 Par Value, Trading Symbol LNT, Nasdaq Global Select Market

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

Alliant Energy Corporation - Yes ☒ No ☐

Interstate Power and Light Company - Yes ☒ No ☐

Wisconsin Power and Light Company - Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Alliant Energy Corporation - Yes ☒ No ☐

Interstate Power and Light Company - Yes ☒ No ☐

Wisconsin Power and Light Company - Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Alliant Energy Corporation - Large Accelerated Filer ☒ Accelerated Filer ☐ Non-accelerated Filer ☐ Smaller Reporting Company ☐ Emerging Growth Company ☐

Interstate Power and Light Company - Large Accelerated Filer ☐ Accelerated Filer ☐ Non-accelerated Filer ☒ Smaller Reporting Company ☐ Emerging Growth Company ☐

Wisconsin Power and Light Company - Large Accelerated Filer ☐ Accelerated Filer ☐ Non-accelerated Filer ☒ Smaller Reporting Company ☐ Emerging Growth Company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

Alliant Energy Corporation ☐

Interstate Power and Light Company ☐

Wisconsin Power and Light Company ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

Alliant Energy Corporation - Yes ☐ No ☒

Interstate Power and Light Company - Yes ☐ No ☒

Wisconsin Power and Light Company - Yes ☐ No ☒

Number of shares outstanding of each class of common stock as of June 30, 2026:

Alliant Energy Corporation, Common Stock, $0.01 par value, 259,284,699 shares outstanding

Interstate Power and Light Company, Common Stock, $2.50 par value, 13,370,788 shares outstanding (all outstanding shares are owned beneficially and of record by Alliant Energy Corporation)

Wisconsin Power and Light Company, Common Stock, $5 par value, 13,236,601 shares outstanding (all outstanding shares are owned beneficially and of record by Alliant Energy Corporation)

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DEFINITIONS

The following abbreviations or acronyms used in this report are defined below:

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FORWARD-LOOKING STATEMENTS

Statements contained in this report that are not of historical fact are forward-looking statements intended to qualify for the safe harbors from liability established by the Private Securities Litigation Reform Act of 1995. These forward-looking statements can be identified as such because the statements include words such as “may,” “believe,” “expect,” “anticipate,” “plan,” “project,” “will,” “projections,” “estimate,” or other words of similar import. Similarly, statements that describe future financial performance or plans or strategies are forward-looking statements. Such forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those expressed in, or implied by, such statements. Some, but not all, of the risks and uncertainties of Alliant Energy, IPL and WPL that could materially affect actual results include:

• IPL’s and WPL’s ability to obtain adequate and timely rate relief to allow for, among other things, recovery of and/or the return on costs, including fuel costs, operating costs, transmission costs, capacity costs, costs of cancelled generation projects incurred prior to pursuing regulatory approval, including costs incurred for generation projects that are delayed, modified or no longer pursued due to changes in resource needs or plans, as well as costs of generation projects incurred prior to regulatory approval or that exceed initial estimates, deferred expenditures, deferred tax assets, tax expense, interest expense, capital expenditures, marginal costs to service new customers, and remaining costs related to electric generating units (EGUs) that have been or may be permanently closed and certain other retired assets, environmental remediation costs, and decreases in sales volumes, as well as earning their authorized rates of return, payments to their parent of expected levels of dividends, the impact of rate design on current and potential customers and demand for energy in their service territories, and the ability to obtain regulatory approval with acceptable conditions for individual customer rates for large load growth customers and WPL’s large load tariff;

• the impact of IPL’s retail electric base rate moratorium;

• the ability to obtain regulatory approval for construction projects with acceptable conditions;

• the ability to complete construction of generation and energy storage projects by planned in-service dates, with the expected earnings contributions and within the cost targets set by regulators due to cost increases of and access to materials, equipment and commodities, which could result from tariffs, including previously exempted tariffs related to solar project materials and equipment from certain countries, duties or other assessments, including antidumping or countervailing duties, inflation, labor issues or supply shortages, supply chain disruptions which may result from geopolitical issues, contractor performance, the ability to successfully resolve warranty issues or contract disputes, the ability to obtain adequate generator interconnection agreements to connect the new projects to MISO in a timely manner, the ability to obtain siting and environmental permits from local and state agencies and the ability of ITC Midwest LLC (ITC) and ATC to complete transmission upgrades in a timely manner;

• weather effects on utility sales volumes and operations;

• the direct or indirect effects resulting from cybersecurity incidents or attacks on Alliant Energy, IPL, WPL, or their suppliers, contractors and partners, or responses to such incidents;

• the impact of customer- and third party-owned generation and other non-traditional service models, including alternative electric suppliers and potential policy changes, regulatory changes, or legislation that may enable large customers to source behind-the-meter generation directly from third parties or to own or otherwise procure on-site or behind-the-meter generation or participate in co-located resource arrangements, in IPL’s and WPL’s service territories on system reliability, operating expenses and customers’ demand for electricity;

• economic conditions in IPL’s and WPL’s service territories, including the potential impacts of business or facility closures and tariffs;

• the ability and cost to attract large load growth customers and to provide sufficient generation and the ability of ITC and ATC to provide sufficient transmission capacity for potential load growth timely, including significant new commercial or industrial customers, such as data centers;

• the ability of potential large load growth customers to timely construct new facilities, due to local or state regulatory actions, zoning, siting, or permitting actions, public or community opposition or other factors, as well as the resulting higher system load demand by expected levels and timeframes;

• the impact of large load growth customers altering, delaying or cancelling planned facilities, including any resulting impacts of overbuilt or under-utilized transmission capacity or generation and energy storage assets;

• the impact of energy efficiency, franchise retention and customer disconnects on sales volumes and operating income;

• the impact that price changes may have on IPL’s and WPL’s customers’ demand for electric and gas services and their ability to pay their bills;

• changes in the price of delivered natural gas, transmission, purchased electric energy, purchased electric capacity and delivered coal, particularly during elevated market prices, and any resulting changes to counterparty credit risk, due to shifts in supply and demand caused by market conditions, regulations and MISO’s seasonal resource adequacy process;

• the ability to achieve the expected level of tax benefits for renewable generation and energy storage projects based on tax guidelines, timely beginning of construction and in-service dates, sourcing permissible amounts of construction and/or financing support from entities with ties to certain foreign countries, compliance with prevailing wage and apprenticeship requirements, project costs and the level of electricity output generated by qualifying generating facilities, and the ability to efficiently utilize the renewable generation and energy storage project tax benefits to achieve IPL’s authorized rate of return and for the benefit of IPL’s and WPL’s customers;

• federal and state regulatory or governmental actions, including the impact of legislation, Treasury regulations, executive orders, interpretations and guidance, and changes in public policy, including changes impacting renewable tax credits, including any repeal, modification, or reduced funding of the Inflation Reduction Act and the One Big Beautiful Bill Act, and siting generation and energy storage projects;

• the ability to utilize tax credits generated to date, and those that may be generated in the future, before they expire, as well as the ability to transfer tax credits that may be generated in the future at adequate pricing;

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• the impacts of changes in the tax code, including tax rates, minimum tax rates, adjustments made to deferred tax assets and liabilities, changes in state income tax apportionment, and changes impacting the availability of and ability to transfer renewable tax credits, including preserving the qualification of any future tax credits;

• disruptions to ongoing operations and the supply of materials, services, equipment and commodities needed to continue to operate and maintain existing assets and to construct capital projects, which may result from geopolitical issues, tariffs, supplier manufacturing constraints, regulatory requirements, labor issues or transportation issues, and thus affect the ability to meet capacity requirements and result in increased capacity expense;

• inflation and higher interest rates;

• continued access to the capital markets on competitive terms and rates, and risks associated with potential increases in borrowing costs or reduced access to funding, and the actions of credit rating agencies;

• the future development of technologies related to electrification, and the ability to reliably store and manage electricity;

• employee workforce factors, including the ability to hire and retain employees with specialized skills, impacts from employee retirements, changes in key executives, ability to create desired corporate culture, collective bargaining agreements and negotiations, work stoppages or restructurings;

• disruptions in the supply and delivery of natural gas, purchased electricity and coal;

• changes to the creditworthiness of, or performance of obligations by, counterparties with which Alliant Energy, IPL and WPL have contractual arrangements, including large load growth customers, participants in the energy markets and fuel suppliers and transporters;

• the impact of penalties or third-party claims related to, or in connection with, a failure to maintain the security of personally identifiable information, including associated costs to notify affected persons and to mitigate their information security concerns;

• impacts that terrorist attacks may have on Alliant Energy’s, IPL’s and WPL’s operations and recovery of costs associated with restoration activities, or on the operations of Alliant Energy’s investments;

• changes to MISO’s interconnection or resource adequacy process establishing capacity planning reserve margin and capacity accreditation requirements that may impact how and when new and existing generating and energy storage facilities may be accredited with energy capacity, and may require IPL and WPL to adjust their current resource plans, to add resources to meet the requirements of MISO’s process or to procure capacity in the market whereby such costs might not be recovered in rates;

• any legislative or regulatory changes that impose mandatory integrated resource planning requirements or materially modify existing planning processes, potentially affecting resource selection, cost recovery, and the ability to meet large load growth demand for energy;

• any material post-closing payments related to any past asset divestitures, including the transfer of renewable tax credits, which could result from, among other things, indemnification agreements, warranties, guarantees or litigation;

• issues associated with environmental remediation and environmental compliance, including compliance with all current environmental and emissions laws, regulations, siting requirements, and permits and future changes in environmental laws and regulations, including the Coal Combustion Residuals Rule, Cross-State Air Pollution Rule and federal, state or local regulations for emissions reductions, including greenhouse gases (GHG), from new and existing fossil-fueled EGUs under the Clean Air Act, and litigation associated with environmental requirements;

• increased pressure from customers, investors and other stakeholders to more rapidly reduce GHG emissions;

• the timely development of technologies, innovations and advancements to provide cost effective alternatives to traditional energy sources;

• the ability to defend against environmental claims brought by state and federal agencies, such as the EPA and state natural resources agencies, or third parties, such as the Sierra Club, and the impact on operating expenses of defending and resolving such claims;

• the direct or indirect effects resulting from breakdown or failure of equipment in the operation of electric and gas distribution systems, such as mechanical problems, disruptions in telecommunications, technological problems, and explosions or fires, and compliance with electric and gas transmission and distribution safety regulations, including regulations promulgated by the Pipeline and Hazardous Materials Safety Administration;

• issues related to the availability and operations of EGUs and energy storage facilities, including start-up risks, breakdown or failure of equipment, fires, availability of warranty coverage and successful resolution of warranty issues or contract disputes for equipment breakdowns or failures, performance below expected or contracted levels of output or efficiency, operator error, employee safety, transmission constraints, compliance with mandatory reliability standards and risks related to recovery of resulting incremental operating, capacity, fuel-related and capital costs through rates;

• impacts that excessive heat, excessive cold, storms, wildfires, or natural disasters may have on Alliant Energy’s, IPL’s and WPL’s operations and construction activities, and recovery of costs associated with restoration activities, or on the operations of Alliant Energy’s investments;

• Alliant Energy’s ability to sustain its dividend payout ratio goal;

• changes to costs of providing benefits and related funding requirements of pension and other postretirement benefits (OPEB) plans due to the market value of the assets that fund the plans, economic conditions, financial market performance, interest rates, timing and form of benefits payments, life expectancies and demographics;

• material changes in employee-related benefit and compensation costs, including settlement losses related to pension plans;

• risks associated with operation and ownership of non-utility holdings, including potential impairments and risks associated with valuation changes of investments;

• changes in technology that alter the channels through which customers buy or utilize Alliant Energy’s, IPL’s or WPL’s products and services;

• risks associated with third-party risk management practices, including vendor financial condition, operational performance, cybersecurity incidents, and compliance with contractual and regulatory requirements;

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• risks associated with large-scale internal technology modernization initiatives, including enterprise asset management systems, operational technology/informational technology integration, cloud transformation, and digital modernization, and the potential for delays, cost overruns, or operational impacts;

• impacts on equity income from unconsolidated investments from changes in valuations of the assets held, as well as potential changes to ATC’s authorized return on equity;

• impacts of IPL’s future tax benefits from Iowa rate-making practices, including deductions for repairs expenditures and cost of removal obligations, allocation of mixed service costs and state depreciation, and recoverability of the associated regulatory assets from customers, when the differences reverse in future periods;

• current or future litigation, regulatory investigations, proceedings or inquiries;

• reputational damage from negative publicity, protests, fines, penalties and other negative consequences resulting in regulatory and/or legal actions;

• the direct or indirect effects resulting from pandemics;

• the effect of accounting standards issued periodically by standard-setting bodies;

• the ability to successfully complete tax audits and changes in tax accounting methods with no material impact on earnings and cash flows; and

• other factors listed in MDA and Risk Factors in Item 1A in the 2025 Form 10-K.

Alliant Energy, IPL and WPL each assume no obligation, and disclaim any duty, to update the forward-looking statements in this report, except as required by law.

Available Information. Alliant Energy routinely posts important information on its website and considers the Investors section of its website, www.alliantenergy.com/investors, a channel of distribution for material information. Information contained on Alliant Energy’s website is not incorporated herein by reference.

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PART I. FINANCIAL INFORMATION

ALLIANT ENERGY CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED)

Refer to accompanying Combined Notes to Condensed Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED)

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This MDA includes information relating to Alliant Energy, and IPL and WPL (collectively, the Utilities), as well as ATC Holdings, AEF and Corporate Services. Where appropriate, information relating to a specific entity has been segregated and labeled as such. The following discussion and analysis should be read in conjunction with the Financial Statements and the Notes included in this report, as well as the financial statements, notes and MDA included in the 2025 Form 10-K. Unless otherwise noted, all “per share” references in MDA refer to earnings per diluted share.

2026 HIGHLIGHTS

Key highlights since the filing of the 2025 Form 10-K include the following:

Customer Investments:

• In March 2026, the IUC approved advance rate-making principles for IPL for up to 1,000 MW of new wind generation in Iowa. The rate-making principles approved include a fixed cost cap of $3,020/kilowatt, including AFUDC and transmission costs, among other costs. IPL’s return on common equity will be the same as other assets without advance rate-making principles for the purposes of setting future rates and IPL’s blended return on common equity, which will be updated each year, will be used for IPL’s retail electric earnings sharing mechanism calculation.

• In March 2026, WPL filed a certificate of authority application with the PSCW for approval to construct, own and install equipment that will maintain and increase the capacity and efficiency of its Riverside Energy Center. A decision from the PSCW is currently expected in the second quarter of 2027.

• In April 2026, IPL filed a certificate of public convenience, use and necessity (GCU Certificate) application with the IUC for approval to construct, own and operate an approximately 720 MW simple-cycle natural gas-fired EGU in Linn County, Iowa. A decision from the IUC is currently expected in the first quarter of 2027.

• In May 2026, IPL filed an application for amendment to its GCU Certificate with the IUC for approval to construct, own and operate up to an additional 125 MW of energy storage at the site of its Whispering Willow - North wind farm. The application seeks to increase the energy storage capacity at the site from the 75 MW previously approved to approximately 200 MW. A decision from the IUC is currently expected in the fourth quarter of 2026.

• In June 2026, the Neenah Unit 2 and Sheboygan Falls Unit 2 advanced gas path projects were completed, which increased the efficiency and capacity at each of these EGUs.

• In July 2026, IPL filed a GCU Certificate application with the IUC for approval to construct, own and operate an approximately 1,200 MW simple-cycle natural gas-fired EGU near the site of its Emery Generating Station, known as the Riverhawk Energy Center. A decision from the IUC is currently expected in the second quarter of 2027.

• In July 2026, the PSCW issued an order authorizing WPL to construct, own and operate the Bent Tree North EGU, an approximately 153 MW wind farm.

Rate Matters:

Large Load Tariff – In connection with its June 2026 approval of an individual customer rate (ICR), the PSCW directed WPL to file a large load tariff applicable to all customers with demand requirements of 100 MW or greater. The tariff must be filed before or concurrently with any future request for approval of an electric service agreement with a customer of 100 MW or greater of demand requirements. The large load tariff must specify the rates, terms and conditions applicable to customers meeting the applicable threshold and describe the standards and protections WPL will apply when evaluating electric service agreements with large load growth customers. In addition, customers served under approved ICRs must be treated as a separate customer class for purposes of future cost-of-service studies in WPL’s next retail electric rate review. The requirement to file a large load tariff did not affect the PSCW’s June 2026 approval of the ICR. Refer to “Growing Customer Demand” for additional information regarding the approved ICR.

Growing Customer Demand:

• In April 2026, IPL entered into an electric service agreement with a customer, who currently expects to build a data center in IPL’s service territory. This electric service agreement includes contracted peak demand of approximately 370 MW. The actual timing and amount of increases in IPL’s load are subject to various factors, including interconnections and actual customer demand, and any executed or future agreements with customers are not expected to result in immediate increases in load.

• In June 2026, the PSCW approved an ICR for a customer who is constructing a data center in WPL’s service territory, subject to certain conditions, including the recognition of demand revenue received prior to WPL’s next retail electric rate review through WPL’s retail electric fuel cost recovery mechanism. Refer to “Rate Matters” for additional information regarding the large load tariff requirements established by the PSCW in connection with its approval of the ICR.

Environmental Matters:

Coal Combustion Residuals (CCR) Rule - In April 2026, the EPA proposed a rule that would significantly reduce the scope of the CCR Rule, which is currently anticipated to be finalized by the end of 2026. Alliant Energy, IPL and WPL continue to evaluate the revised CCR Rule and are unable to predict with certainty the future outcome or impact of these updates, including resolution of ongoing litigation.

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Effluent Limitation Guidelines and Standards (ELGs) - In May 2026, the EPA proposed changes to the 2024 ELG Rule, which are currently anticipated to be finalized by the end of 2026. The proposed rule would revise discharge limits for specific categories of wastewater from certain existing steam EGUs. If finalized, the revised limitations would be implemented in the wastewater discharge permits issued by state agencies to affected facilities. Alliant Energy, IPL and WPL continue to evaluate the revised 2024 ELG Rule and are unable to predict with certainty the future outcome or impact of these updates, including resolution of ongoing or potential litigation.

Legislative Matters:

• In April 2026, the State of Wisconsin enacted 2025 Wisconsin Act 193, which requires utilities to include their capacity costs and revenues in their annual fuel cost plans. The most significant provisions of the legislation for Alliant Energy and WPL are the requirement that fuel cost calculations in approved fuel cost plans account for both the cost of purchasing capacity and the revenue generated from selling it. The legislation applies to fuel cost plans filed on or after January 1, 2027.

RESULTS OF OPERATIONS

Financial Results Overview - The table below includes diluted EPS for Utilities and Corporate Services, ATC Holdings, and Non-utility and Parent, which are non-GAAP financial measures. Alliant Energy believes these non-GAAP financial measures are useful to investors because they facilitate an understanding of per

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Quantitative and Qualitative Disclosures About Market Risk are reported in the 2025 Form 10-K and have not changed materially.

Alliant Energy’s, IPL’s and WPL’s management evaluated, with the participation of each of Alliant Energy’s, IPL’s and WPL’s Chief Executive Officer, Chief Financial Officer and Disclosure Committee, the effectiveness of the design and operation of Alliant Energy’s, IPL’s and WPL’s disclosure controls and procedures (as defined in Rule 13a-15(e) of the Securities Exchange Act of 1934, as amended) as of June 30, 2026 pursuant to the requirements of the Securities Exchange Act of 1934, as amended. Based on their evaluation, the Chief Executive Officer and the Chief Financial Officer concluded that Alliant Energy’s, IPL’s and WPL’s disclosure controls and procedures were effective as of the quarter ended June 30, 2026.

There was no change in Alliant Energy’s, IPL’s and WPL’s internal control over financial reporting that occurred during the quarter ended June 30, 2026 that has materially affected, or is reasonably likely to materially affect, Alliant Energy’s, IPL’s or WPL’s internal control over financial reporting.

PART II. OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS

None. SEC regulations require Alliant Energy, IPL and WPL to disclose information about certain proceedings arising under federal, state or local environmental provisions when a governmental authority is a party to the proceedings and such proceedings involve potential monetary sanctions that Alliant Energy, IPL and WPL reasonably believe will exceed a specified threshold. Pursuant to the SEC regulations, Alliant Energy, IPL and WPL use a threshold of $1 million for purposes of determining whether disclosure of any such proceedings is required. Applying this threshold, there are no environmental matters to disclose for this period.

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The risk factors described in Item 1A in the 2025 Form 10-K have not changed materially.

ITEM 2. UNREGISTERED SALES OF EQUITY SECURITIES AND USE OF PROCEEDS

A summary of Alliant Energy common stock repurchases for the quarter ended June 30, 2026 was as follows:

(a)All shares were purchased on the open market and held in a rabbi trust under the Alliant Energy Deferred Compensation Plan. There is no limit on the number of shares of Alliant Energy common stock that may be held under the Deferred Compensation Plan, which currently does not have an expiration date.

During the quarter ended June 30, 2026, no director or officer of Alliant Energy, IPL or WPL adopted or terminated a Rule 10b5-1 trading arrangement or non-Rule 10b5-1 trading arrangement, as each term is defined in Item 408(a) of Regulation S-K.

Amended and Restated Bylaws

On July 29, 2026, the Board of Directors (the “Board”) of Alliant Energy Corporation (the “Company”) approved an amendment and restatement, effective July 31, 2026 (the “Amendment and Restatement”), of the Amended and Restated Bylaws of the Company, dated November 8, 2022 (the “Bylaws”).

The Amendment and Restatement amends Section 4.4 of the Bylaws to remove provisions relating to (i) the age following which directors are not eligible to be re-elected to the Board and (ii) the process by which a director must provide notice and tender a resignation to the Board following a change in employment, with such topics instead addressed within the Company’s Corporate Governance Guidelines, which are available on the Company’s investor website.

The Amendment and Restatement also amends Section 6.1 of the Bylaws to update the officers required to be elected by the Board to a specified list of officers identified in the Bylaws, together with any executive officers of the Company as defined by the rules and regulations of the Securities and Exchange Commission. Additionally, the Amendment and Restatement contains amendments to Section 6.3 and 6.6, in order to conform to the changes in Section 6.1.

The foregoing description of the Amendment and Restatement does not purport to be complete and is qualified in its entirety by reference to the full text of the Amended and Restated Bylaws, effective July 31, 2026, which is filed as Exhibit 3.1 to this Quarterly Report on Form 10-Q and is incorporated herein by reference.

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The following Exhibits are filed herewith or incorporated herein by reference.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company have each duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized on the 31st day of July 2026.