10-K – 2026-02-20 – lnt-20251231.htm

Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At December 31, 2025 and 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different th an amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:

Alliant Energy IPL WPL
Gross Gross Gross
(as reported) Net (as reported) Net (as reported) Net
2025
Derivative assets $ 69 $ 59 $ 44 $ 40 $ 25 $ 19
Derivative liabilities 51 41 11 7 40 34
2024
Derivative assets 75 64 48 43 27 21
Derivative liabilities 58 47 13 8 45 39

Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Interest Rate Derivative - In January 2023, AEF entered into a $ 300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93 % on a portion of its variable-rate term loan borrowings. In 2025, 2024 and 2023, $ 1 million, $ 4 million and $ 3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statements related to the interest rate swap.

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In October 2025, AEC entered into a $ 300 million forward starting interest rate swap maturing in March 2028 to mitigate forecasted interest rate risk. Under the terms of the swap, AEC exchanged a variable interest rate for a fixed interest rate of 3.10 % on a portion of its forecasted variable-rate term loan borrowings expected to be issued in 2026. The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts. As of December 31, 2025, $ 1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income. As of December 31, 2025, accumulated other comprehensive income included $ 1 million of income related to the interest rate swap. In 2025, there were no increases or reductions to interest expense recorded in Alliant Energy’s income statement related to the interest rate swap.

NOTE 15. FAIR VALUE MEASUREMENTS
Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation.

The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.

Valuation Techniques -
Derivative assets and derivative liabilities - Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using auction prices and were categorized as Level 3. Refer to Note 1 4 for additional details of derivative assets and derivative liabilities.

Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 5(b) for additional information regarding deferred proceeds.

Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on a discounted cash flow methodology using observable data from comparably traded securities with similar credit profiles, and was classified as Level 2. Refer to Note 8 (b) for additional information regarding long-term debt.

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Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy 2025 2024
Fair Value Fair Value
Carrying Level Level Level Carrying Level Level Level
Amount 1 2 3 Total Amount 1 2 3 Total
Assets:
Money market fund investments $ 411   $ 411   $ —   $ —   $ 411   $ 52   $ 52   $ —   $ —   $ 52  

Commodity derivatives 69   —   36   33   69   75   —   48   27   75  
Interest rate derivatives 1   —   1   —   1   1   —   1   —   1  
Deferred proceeds 126   —   —   126   126   163   —   —   163   163  
Liabilities:
Commodity derivatives 51   —   50   1   51   58   —   56   2   58  

Long-term debt (incl. current maturities) 12,028   —   11,748   —   11,748   9,848   —   9,577   —   9,577  

IPL 2025 2024
Fair Value Fair Value
Carrying Level Level Level Carrying Level Level Level
Amount 1 2 3 Total Amount 1 2 3 Total
Assets:
Money market fund investments $ —   $ —   $ —   $ —   $ —   $ 9   $ 9   $ —   $ —   $ 9  
Commodity derivatives 44   —   18   26   44   48   —   26   22   48  
Deferred proceeds 126   —   —   126   126   163   —   —   163   163  
Liabilities:
Commodity derivatives 11   —   10   1   11   13   —   11   2   13  
Long-term debt (incl. current maturities) 4,680   —   4,445   —   4,445   4,090   —   3,736   —   3,736  

WPL 2025 2024
Fair Value Fair Value
Carrying Level Level Level Carrying Level Level Level
Amount 1 2 3 Total Amount 1 2 3 Total
Assets:
Money market fund investments $ 25   $ 25   $ —   $ —   $ 25   $ 43   $ 43   $ —   $ —   $ 43  
Commodity derivatives 25   —   18   7   25   27   —   22   5   27  
Liabilities:
Commodity derivatives 40   —   40   —   40   45   —   45   —   45  
Long-term debt 3,669   —   3,575   —   3,575   3,370   —   3,170   —   3,170  

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy Commodity Contract Derivative
Assets and (Liabilities), net Deferred Proceeds
2025 2024 2025 2024
Beginning balance, January 1 $ 25 $ 24 $ 163 $ 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 11 ( 3 ) — —

Purchases 50 59 — —
Sales ( 3 ) ( 3 ) — —
Settlements (a) ( 51 ) ( 52 ) ( 37 ) ( 53 )
Ending balance, December 31 $ 32 $ 25 $ 126 $ 163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $ 11 ($ 3 ) $ — $ —

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IPL Commodity Contract Derivative
Assets and (Liabilities), net Deferred Proceeds
2025 2024 2025 2024
Beginning balance, January 1 $ 20 $ 19 $ 163 $ 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 5 ( 4 ) — —

Purchases 40 45 — —
Sales ( 2 ) ( 2 ) — —
Settlements (a) ( 38 ) ( 38 ) ( 37 ) ( 53 )
Ending balance, December 31 $ 25 $ 20 $ 126 $ 163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $ 5 ($ 4 ) $ — $ —

WPL Commodity Contract Derivative
Assets and (Liabilities), net
2025 2024
Beginning balance, January 1 $ 5 $ 5
Total net gains included in changes in net assets (realized/unrealized) 6 1

Purchases 10 14
Sales ( 1 ) ( 1 )
Settlements ( 13 ) ( 14 )
Ending balance, December 31 $ 7 $ 5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31 $ 6 $ 1

(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Commodity Contracts - The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

Alliant Energy IPL WPL
Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs
2025 $ 3 $ 29 $ 3 $ 22 $ — $ 7
2024 — 25 — 20 — 5

NOTE 16. COMMITMENTS AND CONTINGENCIES

NOTE 16 (a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility. At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $ 459 million, $ 302 million, and $ 155 million, respectively.

NOTE 16 (b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):

Alliant Energy 2026 2027 2028 2029 2030 Thereafter Total

Natural gas $ 271 $ 191 $ 163 $ 145 $ 103 $ 245 $ 1,118
Coal 76 42 28 — — — 146
Other (a) 57 16 8 4 3 17 105
$ 404 $ 249 $ 199 $ 149 $ 106 $ 262 $ 1,369

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IPL 2026 2027 2028 2029 2030 Thereafter Total

Natural gas $ 149 $ 105 $ 85 $ 70 $ 31 $ 52 $ 492
Coal 34 14 10 — — — 58
Other (a) 24 2 2 2 2 16 48
$ 207 $ 121 $ 97 $ 72 $ 33 $ 68 $ 598

WPL 2026 2027 2028 2029 2030 Thereafter Total

Natural gas $ 122 $ 86 $ 78 $ 75 $ 72 $ 193 $ 626
Coal 42 28 18 — — — 88
Other (a) 25 1 — — — — 26
$ 189 $ 115 $ 96 $ 75 $ 72 $ 193 $ 740

(a) Includes individual commitments incurred during the normal course of business that exceeded $ 1 million at December 31, 2025.

NOTE 16 (c) Legal Proceedings - Alliant Energy, IPL and WPL are involved in legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations.

NOTE 16 (d) Guarantees and Indemnifications -
Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6 % share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of December 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $ 92 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of December 31, 2025 and 2024.

Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $ 35 million as of December 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $ 17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2025 and 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of December 31, 2025, IPL and WPL provided indemnifications associated with $ 333 million and $ 266 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of December 31, 2025, IPL’s and WPL’s related guarantees were approximately $ 130 million and $ 55 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of December 31, 2025.

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NOTE 16 (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites.

Manufactured Gas Plant Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):

Alliant Energy IPL WPL
Range of estimated future costs $ 7   - $ 29 $ 5   - $ 18 $ 2   - $ 11
Current and non-current environmental liabilities $ 12 $ 8 $ 4

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed all of the requirements under the Consent Decree. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including the CAA.

NOTE 16 (f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Illinois and Iowa. WPL provides retail electric and gas services and wholesale electric service in Wisconsin. The geographic concentration of IPL’s and WPL’s customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a large customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or gas services.

Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of generation and transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, different counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and different counterparties, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance.

Refer to Notes 5(a) and 1 4 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.

NOTE 16 (g) Collective Bargaining Agreements - At December 31, 2025, employees covered by collective bargaining agreements represented 58 %, 74 % and 86 % of total employees of Alliant Energy, IPL and WPL, respectively. In May 2026, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expires, representing 29 % and 86 % of total employees of Alliant Energy and WPL, respectively.

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NOTE 17. SEGMENTS OF BUSINESS
Alliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:
• IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.
• WPL - is a utility serving electric and natural gas customers in Wisconsin, and is its own reportable segment as shown in the tables below.

Other, which is not a reportable segment of Alliant Energy, includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF is comprised of Alliant Energy’s interest in ATC Holdings, Travero, a non-utility wind farm, corporate venture investments, the Sheboygan Falls Energy Facility and other non-utility holdings. The “Other” columns are included in the tables below to reconcile to consolidated amounts. Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other. In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures. Previously reported information for prior periods has been recast to conform with the current period presentation.

Alliant Energy’s chief operating decision maker (CODM) is its President and CEO, and IPL’s and WPL’s CODM is their CEO. The CODM uses net income generated from IPL’s and WPL’s operations to assess segment performance, make operating decisions, and allocate resources. Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. There was no single customer whose revenues were 10% or more of Alliant Energy’s, IPL’s and WPL’s respective consolidated revenues. All of Alliant Energy’s, IPL’s and WPL’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):

Utility
Total Alliant
Reportable Energy
2025 IPL WPL Segments Other Consolidated
Electric utility revenues $ 1,896   $ 1,801   $ 3,697   N/A $ 3,697
Gas utility revenues 265   260   525   N/A 525
Other revenues 47   4   51   $ 89 140
Total revenues 2,208   2,065   4,273   89 4,362
Electric production fuel and purchased power expense 283   459   742   N/A 742
Electric transmission service expense 422   203   625   N/A 625
Cost of gas sold expense 130   133   263   N/A 263

Other operation and maintenance expense (a) 373   306   679   61 740
Other segment items:
Depreciation and amortization expense 463   370   833   13 846
Interest expense 211 173 384 128 512
Equity income from unconsolidated investments, net —   ( 2 ) ( 2 ) ( 58 ) ( 60 )
Income tax benefit ( 127 ) ( 14 ) ( 141 ) ( 8 ) ( 149 )
Other (b) ( 4 ) 36 32   1 33
Net income (loss) 457 401 858 ( 48 ) 810
Total assets 12,495   10,655   23,150   1,841 24,991
Investments in equity method subsidiaries 5   19   24   650 674
Construction and acquisition expenditures 1,473   804   2,277   206 2,483

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Utility
Total Alliant
Reportable Energy
2024
IPL WPL Segments Other Consolidated
Electric utility revenues $ 1,747   $ 1,625   $ 3,372   N/A $ 3,372
Gas utility revenues 250   215   465   N/A 465
Other revenues 49   5   54   $ 90 144
Total revenues 2,046   1,845   3,891   90 3,981
Electric production fuel and purchased power expense 269   359   628   N/A 628
Electric transmission service expense 417   196   613   N/A 613
Cost of gas sold expense 123   101   224   N/A 224
Asset valuation charge for IPL’s Lansing Generating Station 60   —  60   N/A 60
Other operation and maintenance expense 358   279   637   39 676
Other segment items:
Depreciation and amortization expense 404   357   761   11 772
Interest expense 177   165   342   107 449
Equity income from unconsolidated investments, net —   ( 2 ) ( 2 ) ( 59 ) ( 61 )
Income tax expense (benefit) ( 129 ) 11   ( 118 ) 4 ( 114 )
Other (b) 5   34   39   5 44
Net income (loss) 362   345   707   ( 17 ) 690
Total assets 11,407   10,106   21,513   1,201 22,714
Investments in equity method subsidiaries 5   17   22   601 623
Construction and acquisition expenditures 1,224   828   2,052   197 2,249

Utility
Total Alliant
Reportable Energy
2023 (amounts may not foot due to rounding)
IPL WPL Segments Other Consolidated
Electric utility revenues $ 1,761   $ 1,584   $ 3,345   N/A $ 3,345
Gas utility revenues 300   240   540   N/A 540
Other revenues 49   3   52   $ 90 142
Total revenues 2,110   1,827   3,937   90 4,027
Electric production fuel and purchased power expense 282   455   737   N/A 736
Electric transmission service expense 420   163   583   N/A 583
Cost of gas sold expense 166   134   300   N/A 299
Other operation and maintenance expense 353   271   624   51 675
Other segment items:
Depreciation and amortization expense 388   280   668   8 676
Interest expense 155   149   304   90 394
Equity income from unconsolidated investments, net —   ( 3 ) ( 3 ) ( 58 ) ( 61 )
Income tax expense (benefit) ( 58 ) 60   2   2 4
Other (b) 38   ( 27 ) 11   5 18
Net income (loss) 366   345   711   ( 8 ) 703
Total assets 10,489   9,634   20,123   1,114 21,237
Investments in equity method subsidiaries 5   16   21   564 585
Construction and acquisition expenditures 712   1,019   1,731   123 1,854

(a) Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $ 16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b) Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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NOTE 18. RELATED PARTIES
Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases were as follows (in millions):

IPL WPL
2025 2024 2023 2025 2024 2023
Corporate Services billings $ 194 $ 183 $ 181 $ 189 $ 171 $ 163
Sales credited 27 — 11 131 84 55
Purchases billed 416 430 431 75 54 35

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):

2025 2024
IPL $ 135 $ 135
WPL 84 64

ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties were as follows (in millions):

2025 2024 2023
ATC billings to WPL $ 162 $ 152 $ 159
WPL billings to ATC 27 16 20

As of December 31, 2025 and 2024, WPL owed ATC net amounts of $ 10 million and $ 10 million, respectively.

WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 9 for discussion of WPL’s Sheboygan Falls Energy Facility lease.

ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE

None.

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ITEM 9A. CONTROLS AND PROCEDURES

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 December 31, 2025 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 December 31, 2025.

There was no change in Alliant Energy’s, IPL’s and WPL’s internal control over financial reporting that occurred during the quarter ended December 31, 2025 that has materially affected, or is reasonably likely to materially affect, Alliant Energy’s, IPL’s or WPL’s internal control over financial reporting.

Management’s Annual Report on Internal Control over Financial Reporting - The management of Alliant Energy, IPL and WPL are responsible for establishing and maintaining adequate internal control over financial reporting, as such term is defined in Rules 13a-15(f) and 15d-15(f) under the Securities Exchange Act of 1934, as amended. Alliant Energy’s, IPL’s and WPL’s internal control over financial reporting is designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with GAAP.

Because of the inherent limitations of internal control over financial reporting, misstatements may not be prevented or detected on a timely basis. Also, projections of any evaluation of the effectiveness of the internal control over financial reporting to future periods are subject to the risk that the controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

Alliant Energy’s, IPL’s and WPL’s management assessed the effectiveness of their respective internal control over financial reporting as of December 31, 2025 using the criteria set forth in Internal Control - Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission. Based on these assessments, Alliant Energy’s, IPL’s and WPL’s management concluded that, as of December 31, 2025, their respective internal control over financial reporting was effective.

Deloitte & Touche LLP, Alliant Energy’s independent registered public accounting firm, has audited Alliant Energy’s internal control over financial reporting. That report is included herein. This report does not include an attestation report of IPL’s and WPL’s independent registered public accounting firm regarding its assessment of IPL’s and WPL’s internal control over financial reporting.

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Shareowners and the Board of Directors of Alliant Energy Corporation:

Opinion on Internal Control over Financial Reporting

We have audited the internal control over financial reporting of Alliant Energy Corporation and subsidiaries (the “Company”) as of December 31, 2025, based on criteria established in Internal Control - Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission (COSO). In our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control - Integrated Framework (2013) issued by COSO.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the consolidated financial statements as of and for the year ended December 31, 2025, of the Company and our report dated February 20, 2026, expressed an unqualified opinion on the Company’s 2025 financial statements.

Basis for Opinion

The Company’s management is responsible for maintaining effective internal control over financial reporting and for its assessment of the effectiveness of internal control over financial reporting, included in the accompanying Management’s Annual Report on Internal Control over Financial Reporting. Our responsibility is to express an opinion on the Company’s internal control over financial reporting based on our audit. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether effective internal control over financial reporting was maintained in all material respects. Our audit included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, testing and evaluating the design and operating effectiveness of internal control based on the assessed risk, and performing such other procedures as we considered necessary in the circumstances. We believe that our audit provides a reasonable basis for our opinion.

Definition and Limitations of Internal Control over Financial Reporting

A company’s internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company’s internal control over financial reporting includes those policies and procedures that (1) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use, or disposition of the company’s assets that could have a material effect on the financial statements.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

/s/ Deloitte & Touche LLP

Milwaukee, Wisconsin
February 20, 2026

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ITEM 9B. OTHER INFORMATION

During the quarter ended December 31, 2025, 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 .

ITEM 9C. DISCLOSURE REGARDING FOREIGN JURISDICTIONS THAT PREVENT INSPECTIONS

None.

PART III

ITEM 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE

The information required by Item 10 relating to directors and nominees for election of directors at the 2026 Annual Meeting of Shareowners, the timely filing of reports under Section 16 of the Securities Exchange Act of 1934, audit committees and audit committee financial experts, insider trading policies and procedures, and Alliant Energy’s Code of Conduct is incorporated herein by reference to the relevant information in the 2026 Alliant Energy Proxy Statement, which will be filed with the SEC within 120 days after the end of Alliant Energy’s fiscal year. Information regarding executive officers of Alliant Energy may be found in Part I of this report under the caption “ Information About Executive Officers .”

IPL and WPL are omitted pursuant to Instruction I(2)(c).

ITEM 11. EXECUTIVE COMPENSATION

The information required by Item 11 for Alliant Energy is incorporated herein by reference to the relevant information in the 2026 Alliant Energy Proxy Statement, which will be filed with the SEC within 120 days after the end of Alliant Energy’s fiscal year.

IPL and WPL are omitted pursuant to Instruction I(2)(c).

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS

Information regarding Alliant Energy’s equity compensation plans as of December 31, 2025 was as follows:

(A) (B) (C)
Number of securities to be Weighted-average Number of securities remaining available
issued upon exercise of exercise price of for future issuance under equity
outstanding options, outstanding options, compensation plans (excluding
Plan Category warrants and rights warrants and rights securities reflected in column (A))
Equity compensation plans approved by shareowners 1,686,388 (a) N/A (b) 6,785,563 (c)
Equity compensation plans not approved by shareowners (d) N/A N/A N/A (e)
1,686,388 N/A 6,785,563

(a) Represents performance shares and restricted stock units granted under the 2020 OIP, all of which are paid out in shares of Alliant Energy’s common stock. The performance share awards reflect an assumed payout at the maximum performance multiplier of 200%. The restricted stock units vest at the expiration of a three-year time-vesting period.
(b) No cash consideration is received when shares are distributed for earned performance shares and restricted stock units. Accordingly, there is no weighted-average exercise price.
(c) All of the available shares under the 2020 OIP may be issued as awards in the form of shares of Alliant Energy’s common stock, restricted stock, restricted stock units, performance shares, performance units and other stock-based or cash-based awards. As of December 31, 2025, there were performance shares and restricted stock units outstanding under the 2020 OIP, the only plan under which such equity awards are currently granted.
(d) As of December 31, 2025, there were 367,338 shares of Alliant Energy’s common stock held under the DCP, which is described in Note 1 2 (c) .
(e) There is no limit on the number of shares of Alliant Energy’s common stock that may be held under the DCP.

The remainder of the information required by Item 12 for Alliant Energy is incorporated herein by reference to the relevant information in the 2026 Alliant Energy Proxy Statement, which will be filed with the SEC within 120 days after the end of Alliant Energy’s fiscal year.

IPL and WPL are omitted pursuant to Instruction I(2)(c).

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ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE

The information required by Item 13 for Alliant Energy is incorporated herein by reference to the relevant information in the 2026 Alliant Energy Proxy Statement, which will be filed with the SEC within 120 days after the end of Alliant Energy’s fiscal year.

IPL and WPL are omitted pursuant to Instruction I(2)(c).

ITEM 14. PRINCIPAL ACCOUNTING FEES AND SERVICES

ALLIANT ENERGY
The information required by Item 14 is incorporated herein by reference to the relevant information in the 2026 Alliant Energy Proxy Statement, which will be filed with the SEC within 120 days after the end of Alliant Energy’s fiscal year.

IPL AND WPL
Each of IPL’s and WPL’s Audit Committee of the Board of Directors has adopted a policy that requires advance approval of all audit, audit-related, tax and other permitted services performed by the independent registered public accounting firm. The policy provides for pre-approval by the Audit Committee of specifically defined audit and non-audit services after the Audit Committee is provided with the appropriate level of details regarding the specific services to be provided. The policy does not permit delegation of the Audit Committee’s authority to management. In the event the need for specific services arises between Audit Committee meetings, the Audit Committee has delegated to the Chairperson of the Audit Committee authority to approve permitted services provided that the Chairperson reports any decisions to the Audit Committee at its next scheduled meeting. The principal accounting fees billed to Alliant Energy by its independent registered public accounting firm, all of which were approved in advance by the Audit Committee, directly related and allocated to IPL and WPL were as follows (in thousands):

IPL WPL
2025 2024 2025 2024
Fees % of Total Fees % of Total Fees % of Total Fees % of Total
Audit fees $1,479 96% $1,412 96% $1,294 90% $1,242 92%
Audit-related fees 61 4% 59 4% 137 10% 103 8%
Tax fees 4 —% 3 —% 4 —% 3 —%
All other fees 2 —% 3 —% 2 —% 2 —%
$1,546 100% $1,477 100% $1,437 100% $1,350 100%

IPL’s and WPL’s audit fees for 2025 and 2024 consisted of the respective fees billed for the audits of the financial statements of IPL and its subsidiaries and WPL and its subsidiaries, for reviews of financial statements included in Form 10-Q filings, and for services normally provided in connection with statutory and regulatory filings, such as financing transactions. IPL’s and WPL’s audit fees also included their respective portion of fees for the 2025 and 2024 audits of Alliant Energy’s financial statements and effectiveness of internal controls over financial reporting. IPL’s and WPL’s audit-related fees for 2025 and 2024 consisted of the fees billed for services rendered related to employee benefits plan audits, other attest services and WPL’s audit-related fees for 2025 also included an audit of expenditures of federal awards for the Department of Energy. IPL’s and WPL’s tax fees for 2025 and 2024 consisted of the fees billed for professional services rendered for tax compliance. All other fees for 2025 and 2024 for IPL and WPL consisted of license fees for accounting research software products and seminars. The Audit Committee does not consider the provision of non-audit services by the independent registered public accounting firm described above to be incompatible with maintaining independence of the independent registered public accounting firm.

PART IV

ITEM 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES

(1) Consolidated Financial Statements - Refer to Item 8 Financial Statements and Supplementary Data for Alliant Energy’s, IPL’s and WPL’s financial statements and Reports of Independent Registered Public Accounting Firm (Public Company Accounting Oversight Board ID No. 34 ).

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(2) Financial Statement Schedules -

SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS

ALLIANT ENERGY CORPORATION (Parent Company Only) Year Ended December 31,
CONDENSED STATEMENTS OF INCOME 2025 2024 2023
(in millions)

Operating expenses $ 4   $ 3   $ 3  
Operating loss ( 4 ) ( 3 ) ( 3 )
Other (income) and deductions:
Equity earnings from consolidated subsidiaries ( 863 ) ( 734 ) ( 742 )
Interest expense 57   40   34  
Other ( 3 ) 5   4  
Total other (income) and deductions ( 809 ) ( 689 ) ( 704 )
Income before income taxes 805   686   701  
Income tax benefit ( 6 ) ( 3 ) ( 5 )
Net income $ 811   $ 689   $ 706  

Refer to accompanying Notes to Condensed Financial Statements.

ALLIANT ENERGY CORPORATION (Parent Company Only) December 31,
CONDENSED BALANCE SHEETS 2025 2024
(in millions)
ASSETS
Current assets:
Cash and cash equivalents $ 512   $ —  
Notes receivable from affiliated companies 114   103  
Income tax refunds receivable 12   12  
Other 6   2  
Total current assets 644   117  
Investments:
Investments in consolidated subsidiaries 9,784   9,123  
Other 1   1  
Total investments 9,785   9,124  
Other assets 102   84  
Total assets $ 10,531   $ 9,325  

LIABILITIES AND EQUITY
Current liabilities:
Current maturities of long-term debt $ 574   $ 571  
Commercial paper —   325  
Notes payable to affiliated companies 1,300   1,401  
Other 21   10  
Total current liabilities 1,895   2,307  
Long-term debt, net (excluding current portion) 1,286   —  
Other liabilities 4   3  
Common equity:
Common stock and additional paid-in capital 3,104   3,063  
Retained earnings 4,255   3,965  
Accumulated other comprehensive income 1   1  
Shares in deferred compensation trust ( 14 ) ( 14 )
Total common equity 7,346   7,015  
Total liabilities and equity $ 10,531   $ 9,325  

Refer to accompanying Notes to Condensed Financial Statements.

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ALLIANT ENERGY CORPORATION (Parent Company Only) Year Ended December 31,
CONDENSED STATEMENTS OF CASH FLOWS 2025 2024 2023
(in millions)
Net cash flows from operating activities $ 529   $ 355   $ 445  
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries ( 365 ) ( 380 ) ( 325 )

Net change in notes receivable from and payable to affiliates ( 113 ) 326   ( 281 )

Net cash flows used for investing activities ( 478 ) ( 54 ) ( 606 )
Cash flows from (used for) financing activities:
Common stock dividends ( 521 ) ( 492 ) ( 456 )
Proceeds from issuance of common stock, net 23   23   246  
Proceeds from issuance of long-term debt 1,286   —   565  

Net change in commercial paper ( 325 ) 168   ( 195 )
Other ( 2 ) —   1  
Net cash flows from (used for) financing activities 461   ( 301 ) 161  
Net increase (decrease) in cash, cash equivalents and restricted cash 512   —   —  
Cash, cash equivalents and restricted cash at beginning of period —   —   —  
Cash, cash equivalents and restricted cash at end of period $ 512   $ —   $ —  
Supplemental cash flows information:
Cash (paid) received during the period for:
Interest ($ 45 ) ($ 40 ) ($ 27 )
Income taxes, net:
Federal $ 4   $ 11   $ 8  
State - Iowa —   ( 15 ) ( 13 )
State - Wisconsin —   12   27  
Total income taxes, net $ 4   $ 8   $ 22  

Refer to accompanying Notes to Condensed Financial Statements.

ALLIANT ENERGY CORPORATION (Parent Company Only)
NOTES TO CONDENSED FINANCIAL STATEMENTS

Pursuant to rules and regulations of the SEC, the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only) do not reflect all of the information and notes normally included with financial statements prepared in accordance with GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the Financial Statements and related Notes included in the combined 2025 Form 10-K, Part II, Item 8 , which is incorporated herein by reference.

In the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only), investments in subsidiaries are accounted for using the equity method.

NOTE: All other schedules are omitted because they are not applicable or not required, or because that required information is shown either in the financial statements or in the notes thereto.

(3)     Exhibits Required by SEC Regulation S-K - Pursuant to Item 601(b)(4)(iii) of Regulation S-K, the registrants agree to furnish to the SEC, upon request, any instrument defining the rights of holders of unregistered long-term debt not filed as an exhibit to this combined Form 10-K. No such instrument authorizes securities in excess of 10% of the total assets of Alliant Energy, IPL or WPL, as the case may be. The following exhibits for Alliant Energy, IPL and WPL are filed herewith or incorporated herein by reference.

Exhibit Number Description
3.1 Restated Articles of Incorporation of Alliant Energy, as amended (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Registration Statement on Form S-8 (Reg. No. 333-117654))

3.1a Articles of Amendment to Restated Articles of Incorporation of Alliant Energy, as amended, effective May 4, 2016 (incorporated by reference to Exhibit 3.1 to Alliant Energy’s Form 10-Q for the quarter ended March 31, 2016 (File No. 1-9894))

3.2 Amended and Restated Bylaws of Alliant Energy, effective November 8, 2022 (incorporated by reference to Exhibit 3.1 to Alliant Energy’s Form 10-Q for the quarter ended September 30, 2022 (File No. 1-9894))

3.3 Amended and Restated Articles of Incorporation of WPL, effective May 9, 2013 (incorporated by reference to Exhibit 3.4 to WPL’s Form 8-K, filed May 13, 2013 (File No. 0-337))

3.4 Amended and Restated Bylaws of WPL, effective October 27, 2020 (incorporated by reference to Exhibit 3.3 to WPL’s Form 8-K, filed October 29, 2020 (File No. 0-337))

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Exhibit Number Description
3.5 Amended and Restated Articles of Incorporation of IPL, effective December 20, 2021 (incorporated by reference to Exhibit 3.1 to IPL’s Form 8-K, filed December 21, 2021 (File No. 1-4117))

3.6 Amended and Restated Bylaws of IPL, effective October 27, 2020 (incorporated by reference to Exhibit 3.2 to IPL’s Form 8-K, filed October 29, 2020 (File No. 1-4117))

4.1 Amended and Restated Five-Year Master Credit Agreement, effective December 17, 2021 , among Alliant Energy, IPL, WPL, Wells Fargo Bank, National Association (N.A.) and the lender parties set forth therein (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed December 21, 20 21 (File No. 1-9894))

4.1a First Amendment to Amended and Restated Five-Year Master Credit Agreement, effective March 15, 2023, among Alliant Energy, IPL, WPL, Wells Fargo Bank, N ational A ssociat ion and the lender parties set forth therein (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 10 - Q for the quarter ended March 31, 202 3 (File No. 1-9894))

4.1b Second Amendment to Amended and Restated Five-Year Master Credit Agreement, effective December 18, 2024, among Alliant Energy, IPL, WPL, Wells Fargo Bank, N atio nal A s sociation and the lender parties set forth therein (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K filed December 18, 2024 (File No. 1-9894))

4.1c Extension and Third Amendment to Amended and Restated Five-Year Master Credit Agreement, effective December 18, 2025, among Alliant Energy, IPL, WPL, Wells Fargo Bank, National Association and the lender parties set forth therein

4.2 Indenture, dated as of March 2, 2023, between Alliant Energy and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy's Form 8-K, filed March 3, 2023 (File No. 1-9894))

4.3 Indenture, dated as of May 15, 2025, between Alliant Energy and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed May 15, 2025 (File No. 1-9894))

4.4 Indenture, dated as of September 26, 2025, between Alliant Energy and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed September 26, 2025 (File No. 1-9894))

4.4a First Supplemental Indenture, dated as of September 26, 2025, between Alliant Energy and The Bank of New York Mellon Trust Company, N.A., as trustee, relating to the 5.750% Fixed-to-Fixed Reset Rate Junior Subordinated Notes due 2056 (incorporated by reference to Exhibit 4.2 to Alliant Energy’s Form 8-K, filed September 26, 2025 (File No. 1-9894))

4.5 Indenture, dated as of June 12, 2018, among AEF, Alliant Energy, as guarantor, and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed June 12, 2018 (File No. 1-9894))

4.6 Indenture, dated as of November 20, 2020, among AEF, Alliant Energy as guarantor, and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed November 23, 2020 (File No. 1-9894)

4.7 Indenture, dated as of February 28, 2022, among AEF, Alliant Energy, as guarantor, and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy’s Form 8-K, filed March 1, 2022 (File No. 1-9894))

4.8 Indenture, dated as of November 10, 2023, among AEF, Alliant Energy, as guarantor, and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy's Form 8-K, filed November 13, 2023 (File No. 1-9894))

4.9 Indenture, dated as of June 6, 2024, among AEF, Alliant Energy, as guarantor, and The Bank of New York Mellon Trust Company, N.A., as trustee (incorporated by reference to Exhibit 4.1 to Alliant Energy ’ s Form 8-K, filed June 6, 2024 (File No. 1-9894))

4.10 Indenture, dated as of June 20, 1997, between WPL and U.S. Bank Trust Company, N. A., Successor, as Trustee (incorporated by reference to Exhibit 4.33 to Amendment No. 2 to WPL’s Registration Statement on Form S-3 (Reg. No. 033-60917))

4.10a First Supplemental Indenture, dated September 16, 2021, among WPL, Wells Fargo Bank, National Association, as Original Trustee, and U.S. Bank National Association, as Series Trustee (incorporated by reference to Exhibit 4.1 to WPL's Form 8-K, filed September 16, 2021 (File No. 0-337))

4.11 Officers’ Certificate, dated as of July 28, 2004, creating WPL’s 6.25% Debentures due July 31, 2034 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed August 2, 2004 (File No. 0-337))

4.12 Officers’ Certificate, dated as of August 8, 2007, creating WPL’s 6.375% Debentures due August 15, 2037 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed August 9, 2007 (File No. 0-337))

4.13 Officer s ’ Certificate, dated as of October 1, 2008, creating WPL’s 7.60% Debentures due October 1, 2038 (incorporated by reference to Exhibit 4.2 to WPL’s Form 8-K, filed October 2, 2008 (File No. 0-337))

4.14 Officers’ Certificate, dated as of October 14, 2014, creating WPL’s 4.10% Debentures due October 15, 2044 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed October 14, 2014 (File No. 0-337))

4.15 Officers’ Certificate, dated as of October 10, 2017, creating WPL’s 3.05% Debentures due October 15, 2027 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed October 10, 2017 (File No. 0-337))

4.16 Officers’ Certificate, dated as of June 24, 2019, creating WPL’s 3.00% Debentures due July 1, 2029 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed June 24, 2019 (File No. 0-337))

4.17 Officers’ Certificate, dated as of April 2, 2020, creating WPL’s 3.65% Debentures due April 1, 2050 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed April 2, 2020 (File No. 0-337))

4.18 Officers’ Certificate, dated as of August 15, 2022, creating WPL’s 3.950% Debentures due September 1, 2032 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed August 15, 2022 (File No. 0-337))

4.19 Officers’ Certificate, dated as of March 30, 2023, creating WPL's 4.950% Debentures due April 1, 2033 (incorporated by reference to Exhibit 4.1 to WPL's Form 8-K, filed March 30, 2023 (File No. 0-337))

4.20 Officers’ Certificate, dated as of March 7, 2024, creating WPL’s 5.375% Debentures due March 30, 2034 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed March 7, 2024 (File No. 0-337))

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Exhibit Number Description
4.21 Officers’ Certificate, dated December 5, 2025, creating WPL’s 5.700% Debentures due 2055 (incorporated by reference to Exhibit 4.1 to WPL’s Form 8-K, filed December 5, 2025 (File No. 0-337))

4.22 Indenture (For Senior Unsecured Debt Securities), dated as of August 20, 2003, between IPL and The Bank of New York Mellon Trust Co., N.A. (f/k/a The Bank of New York Trust Co., N.A.), as Trustee (incorporated by reference to Exhibit 4.11 to IPL’s Registration Statement on Form S-3 (Reg. No. 333-108199))

4.23 Officer’s Certificate, dated as of October 14, 2003, creating IPL’s 6.45% Senior Debentures due October 15, 2033 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed October 15, 2003 (File No. 1-4117))

4.24 Officer’s Certificate, dated as of May 3, 2004, creating IPL’s 6.30% Senior Debentures due May 1, 2034 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed May 5, 2004 (File No. 1-4117))

4.24a Officer’s Certificate, dated as of August 2, 2004, reopening IPL’s 6.30% Senior Debentures due May 1, 2034 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed August 5, 2004 (File No. 1-4117))

4.25 Officer’s Certificate, dated as of July 7, 2009, creating IPL’s 6.25% Senior Debentures due July 15, 2039 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed July 8, 2009 (File No. 1-4117))

4.26 Officer’s Certificate, dated as of October 8, 2013, creating IPL’s 4.70% Senior Debentures due October 15, 2043 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed October 8, 2013 (File No. 1-4117))

4.27 Officer’s Certificate, dated as of September 15, 2016, creating IPL’s 3.70% Senior Debentures due September 15, 2046 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 15, 2016 (File No. 1-4117))

4.28 Officer’s Certificate, dated as of September 26, 2018, creating IPL’s 4.10% Senior Debentures due September 26, 2028 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 26, 2018 (File No. 1-4117))

4.29 Officer’s Certificate, dated as of April 1, 2019, creating IPL’s 3.60% Senior Debentures due April 1, 2029 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed April 1, 2019 (File No. 1-4117))

4.30 Officer’s Certificate, dated as of September 26, 2019, creating IPL’s 3.50% Senior Debentures due September 30, 2049 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 26, 2019 (File No. 1-4117))

4.31 Officer’s Certificate, dated as of June 2, 2020, creating IPL’s 2.3% Senior Debentures due June 1, 2030 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed June 2, 2020 (File No. 1-4117))

4.32 Officer’s Certificate, dated as of November 19, 2021, creating IPL’s 3.1% Senior Debentures due November 30, 2051 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed November 19, 2021 (File No. 1-4117))

4.33 Officer’s Certificate, dated as of September 21, 2023, creating IPL’s 5.70% Senior Debentures due October 15, 2033 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 21, 2023 (File No. 1-4117))

4.34 Officer’s Certificate, dated as of September 6, 2024, creating IPL’s 4.950% Senior Debentures due September 30, 2034 and IPL’s 5.450% Senior Debentures due September 30, 2054 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 6, 2024 (File No. 1-4117))

4.35 Officer’s Certificate, dated as of May 19, 2025, creating IPL’s 5.600% Senior Debentures due June 29, 2035 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed May 19, 2025 (File No. 1-4117))

4.36 Officer’s Certificate, dated as of September 11, 2025, creating IPL’s 5.600% Senior Debentures due October 1, 2055 (incorporated by reference to Exhibit 4.1 to IPL’s Form 8-K, filed September 11, 2025 (File No. 1-4117))

4.37 Description of Common Stock of Alliant Energy (incorporated by reference to Exhibit 4.32 to Alliant Energy ’ s Form 10-K for the year 2023 (File No. 1-9894))

10.1 Second Amended and Restated Term Loan Credit Agreement, dated as of March 3, 2025, among AEF, Alliant Energy, U.S. Bank National Association and the lender parties set forth therein (incorporated by reference to Exhibit 10.1 to Alliant Energy’s Form 8-K, filed March 3, 2025 (File No. 1-9894))

10.2# 2020 O I P (incorporated by reference to Appendix A to Alliant Energy’s definitive proxy statement filed on Schedule 14A on April 9, 2020 (File No. 1-9894))

10.2a# Form of Performance Share Agreement pursuant to the 2020 OIP, amended in 2022 (incorporated by reference to Exhibit 10.3d to Alliant Energy’s Form 10-K for the year 2021 (File No. 1-9894))

10.2b# Form of Restricted Stock Unit Agreement pursuant to the 2020 OIP, amended in 2022 (incorporated by reference to Exhibit 10.3e to Alliant Energy’s Form 10-K for the year 2021 (File No. 1-9894))

10.2c# Form of Performance Restricted Stock Unit Agreement (Workforce Composition Metric) pursuant to the 2020 OIP, amended in 2022 (incorporated by reference to Exhibit 10.3f to Alliant Energy’s Form 10-K for the year 2021 (File No. 1-9894))

10.2d# Form of Performance Restricted Stock Unit Agreement (Net Income Metric) pursuant to the 2020 OIP, amended in 2022 (incorporated by reference to Exhibit 10.3g to Alliant Energy’s Form 10-K for the year 2021 (File No. 1-9894))

10.2e# Form of Performance Share Agreement pursuant to the 2020 OIP, amended in 2024 (incorporated by reference to Exhibit 10.2h to Alliant Energy’s Form 10-K for the year 2023 (File No. 1-9894))

10.2f# Form of Performance Share Agreement pursuant to the 2020 OIP, amended in 2025 (incorporated by reference to Exhibit 10.2f to Alliant Energy's Form 10-K for the year 2024 (File No. 1-9894))

10.2g# Form of Restricted Stock Unit Agreement pursuant to the 2020 OIP, amended in 2025 (incorporated by reference to Exhibit 10.2g to Alliant Energy's Form 10-K for the year 2024 (File No. 1-9894))

10.3# DCP, as amended and restated effective November 1, 2024 (incorporated by reference to Exhibit 10.3 to Alliant Energy's Form 10-K for the year 2024 (File No. 1-9894))

10.4# Alliant Energy Rabbi Trust Agreement for DCPs (incorporated by reference to Exhibit 10.19 to Alliant Energy’s Form 10-K for the year 2005 (File No. 1-9894))

10.4a# Amendment to the Alliant Energy Rabbi Trust Agreement for DCPs (incorporated by reference to Exhibit 10.2 to Alliant Energy’s Form 10-Q for the quarter ended June 30, 2015 (File No. 1-9894))

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Exhibit Number Description
10.4b# Second Amendment to the Alliant Energy Rabbi Trust Agreement for DCPs (incorporated by reference to Exhibit 10.3 to Alliant Energy’s Form 10-Q for the quarter ended June 30, 2015 (File No. 1-9894))

10.5# Alliant Energy Excess Retirement Plan (incorporated by reference to Exhibit 10.1 to Alliant Energy’s Form 10-Q for the quarter ended September 30, 2008 (File No. 1-9894))

10.5a# Amendment to the Alliant Energy Excess Retirement Plan (incorporated by reference to Exhibit 10.4 to Alliant Energy’s Form 8-K, filed December 5, 2011 (File No. 1-9894))

10.6# Form of Key Executive Employment and Severance Agreement (KEESA), by and between Alliant Energy and L.M. Barton (incorporated by reference to Exhibit 10.1 to Alliant Energy’s Form 8-K, filed October 28, 2021 (File No. 1-9894))

10.7# Form of KEESA, by and between Alliant Energy and each of R.J. Durian, D.A. de Leon, M.N. Farlinger, R. Sundararajan, A.P. Smyth and R.C. Valcq (incorporated by reference to Exhibit 10.2 to Alliant Energy’s Form 8-K, filed October 28, 2021 (File No. 1-9894))

10.8# Executive Officer Severance Benefit Plan, as amended and restated, effective October 29, 2018 (incorporated by reference to Exhibit 10.1 to Alliant Energy’s Form 10-Q for the quarter ended September 30, 2018 (File No. 1-9894))

10.9# Terms of Alliant Energy Executive Short-term Incentive Plan (incorporated by reference to Exhibit 10.11 to Alliant Energy's Form 10-K for the year 2024 (File No. 1-9894))

10.10# Form of Sign-On Bonus Reimbursement Agreement (incorporated by reference to Exhibit 10.14 to Alliant Energy ’ s Form 10-K for the year 2022 (File No . 1-9894))

10.11# Form of Relocation Reimbursement Agreement (incorporated by reference to Exhibit 10.13 to Alliant Energy ’ s Form 10-K for the year 2023 (File No. 1-9894))

10.12# Summary of Compensation and Benefits for Non-Employee Directors of Alliant Energy, IPL and WPL, effective January 1, 2026

19 Alliant Energy Insider Trading Policies and Procedures (incorporated by reference to Exhibit 19 to Alliant Energy’s Form 10-K for the year 2024 (File No. 1-9894))

21.1 Subsidiaries of Alliant Energy

23.1 Consent of Independent Registered Public Accounting Firm for Alliant Energy

23.2 Consent of Independent Registered Public Accounting Firm for IPL

23.3 Consent of Independent Registered Public Accounting Firm for WPL

31.1 Certification of the Chief Executive Officer for Alliant Energy

31.2 Certification of the Chief Financial Officer for Alliant Energy

31.3 Certification of the Chief Executive Officer for IPL

31.4 Certification of the Chief Financial Officer for IPL

31.5 Certification of the Chief Executive Officer for WPL

31.6 Certification of the Chief Financial Officer for WPL

32.1 Written Statement of the Chief Executive Officer and Chief Financial Officer Pursuant to 18 U.S.C.§1350 for Alliant Energy

32.2 Written Statement of the Chief Executive Officer and Chief Financial Officer Pursuant to 18 U.S.C.§1350 for IPL

32.3 Written Statement of the Chief Executive Officer and Chief Financial Officer Pursuant to 18 U.S.C.§1350 for WPL

97 Alliant Energy Incentive Compensation Recovery Policy (incorporated by reference to Exhibit 97 to Alliant Energy’s Form 10-K for the year ended 2023 (File No. 1-9894))

101.INS Inline XBRL Instance Document - the instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the Inline XBRL document
101.SCH Inline XBRL Taxonomy Extension Schema Document
101.CAL Inline XBRL Taxonomy Extension Calculation Linkbase Document
101.LAB Inline XBRL Taxonomy Extension Label Linkbase Document
101.PRE Inline XBRL Taxonomy Extension Presentation Linkbase Document
101.DEF Inline XBRL Taxonomy Extension Definition Linkbase Document
104 Cover Page Interactive Data File (embedded within the Inline XBRL document)

# A management contract or compensatory plan or arrangement.

ITEM 16. FORM 10-K SUMMARY

None.

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SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Registrants have duly caused this report to be signed on their behalf by the undersigned, thereunto duly authorized on the 20th day of February 2026.

ALLIANT ENERGY INTERSTATE POWER WISCONSIN POWER
CORPORATION AND LIGHT COMPANY AND LIGHT COMPANY
By: /s/ Lisa M. Barton
By: /s/ Lisa M. Barton
By: /s/ Lisa M. Barton

Lisa M. Barton Lisa M. Barton Lisa M. Barton
President and Chief Executive Officer Chief Executive Officer Chief Executive Officer

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the Registrants and in the capacities indicated on the 20th day of February 2026.

ALLIANT ENERGY INTERSTATE POWER WISCONSIN POWER
CORPORATION AND LIGHT COMPANY AND LIGHT COMPANY
/s/ Lisa M. Barton
/s/ Lisa M. Barton
/s/ Lisa M. Barton

Lisa M. Barton Lisa M. Barton Lisa M. Barton
President, Chief Executive Officer and Director (Principal Executive Officer) Chief Executive Officer and Director (Principal Executive Officer) Chief Executive Officer and Director (Principal Executive Officer)

/s/ Robert J. Durian
/s/ Robert J. Durian
/s/ Robert J. Durian

Robert J. Durian Robert J. Durian Robert J. Durian
Executive Vice President and Chief Financial Officer (Principal Financial Officer) Executive Vice President and Chief Financial Officer (Principal Financial Officer) Executive Vice President and Chief Financial Officer (Principal Financial Officer)

/s/ Dylan M. Syse
/s/ Dylan M. Syse
/s/ Dylan M. Syse

Dylan M. Syse Dylan M. Syse Dylan M. Syse
Chief Accounting Officer and Controller (Principal Accounting Officer) Chief Accounting Officer and Controller (Principal Accounting Officer) Chief Accounting Officer and Controller (Principal Accounting Officer)

/s/ Patrick E. Allen
/s/ Patrick E. Allen
/s/ Patrick E. Allen

Patrick E. Allen, Board Chair and Director Patrick E. Allen, Board Chair and Director Patrick E. Allen, Board Chair and Director

/s/ Ignacio A. Cortina
/s/ Ignacio A. Cortina
/s/ Ignacio A. Cortina

Ignacio A. Cortina, Director
Ignacio A. Cortina, Director
Ignacio A. Cortina, Director

/s/ Stephanie L. Cox
/s/ Stephanie L. Cox
/s/ Stephanie L. Cox

Stephanie L. Cox, Director
Stephanie L. Cox, Director
Stephanie L. Cox, Director

/s/ N. Joy Falotico
/s/ N. Joy Falotico
/s/ N. Joy Falotico

N. Joy Falotico, Director
N. Joy Falotico, Director
N. Joy Falotico, Director

/s/ Michael D. Garcia
/s/ Michael D. Garcia
/s/ Michael D. Garcia

Michael D. Garcia, Director
Michael D. Garcia, Director
Michael D. Garcia, Director

/s/ Roger K. Newport
/s/ Roger K. Newport
/s/ Roger K. Newport

Roger K. Newport, Director
Roger K. Newport, Director
Roger K. Newport, Director

/s/ Thomas F. O’Toole
/s/ Thomas F. O’Toole
/s/ Thomas F. O’Toole

Thomas F. O’Toole, Director
Thomas F. O’Toole, Director
Thomas F. O’Toole, Director

/s/ Christie Raymond
/s/ Christie Raymond
/s/ Christie Raymond

Christie Raymond, Director
Christie Raymond, Director
Christie Raymond, Director

/s/ Carol P. Sanders
/s/ Carol P. Sanders
/s/ Carol P. Sanders

Carol P. Sanders, Director
Carol P. Sanders, Director
Carol P. Sanders, Director

116