美国联合能源 2025年度报告

ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year endedDecember31, 2025 or TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _____________ to _____________ Commission File Number: 1-9894 A.Full title of the plan and address of the plan, if different from that of the issuer named below: ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN B.Name of issuer of the securities held pursuant to the plan and the address of its principal executive office: ALLIANT ENERGY CORPORATION4902 North Biltmore LaneMadison, Wisconsin 53718 REQUIRED INFORMATION The following financial statements and schedules of the Alliant Energy Corporation 401(k) Savings Plan, prepared in accordance withthe financial reporting requirements of the Employee Retirement Income Security Act of 1974, as amended, are filed herewith. ALLIANT ENERGY CORPORATION401(k) SAVINGS PLAN TABLE OF CONTENTS REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM FINANCIAL STATEMENTS Statements of Net Assets Available for Benefits as of December31, 2025 and 2024Statement of Changes in Net Assets Available for Benefits for the Year Ended December31, 2025 NOTES TO FINANCIAL STATEMENTS 1. Description of the Plan2. Summary of Significant Accounting Policies3. Tax Status4. Plan Termination Provisions5. Withdrawals and Distributions6. Fair Value Measurements7. Related Party Transactions and Exempt Parties in Interest Transactions8. Nonexempt Parties in Interest Transactions9. Reconciliation to Form 5500 SUPPLEMENTAL SCHEDULESForm 5500, Schedule H, Part IV, line 4a - Schedule of Delinquent Participant Contributions for the year ended December31, 2025 Form 5500, Schedule H, Part IV, line 4i - Schedule of Assets (Held at End of Year) as of December31, 2025Note: All other schedules required by Section 2520.103-10 of the Department of Labor’s Rules and Regulations forReporting and Disclosure under the Employee Retirement Income Security Act of 1974 have been omitted because SIGNATURES EXHIBIT INDEX CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM To the Plan Participants and the Plan Administrator of Alliant Energy Corporation 401(k) Savings Plan Opinion on the Financial Statements We have audited the accompanying statements of net assets available for benefits of the Alliant Energy Corporation 401(k) SavingsPlan (the "Plan") as of December 31, 2025 and 2024, the related statement of changes in net assets available for benefits for the yearended December 31, 2025, and the related notes (collectively referred to as the "financial statements"). In our opinion, the financialstatements present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2025 and 2024, Basis for Opinion These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on the Plan'sfinancial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the auditto obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud.Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to erroror fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence Report on Supplemental Schedules The supplemental schedules of assets (held at end of year) as of December31, 2025 and of delinquent participant contributions for theyear ended December 31, 2025 have been subjected to audit procedures performed in conjunction with the audit of the Plan's financialstatements. The supplemental schedules are the responsibility of the Plan's management. Our audit procedures included determiningwhether the supplemental schedules reconcile to the financial statements or the underlying accounting and other records, as applicable, /s/ DELOITTE & TOUCHE LLP Milwaukee, WIJune16, 2026 ALLIANT ENERGY CORPORATION401(k) SAVINGS PLAN NOTES TO FINANCIAL STATEMENTSAS OF DECEMBER 31, 2025 AND 2024 AND NOTE 1. DESCRIPTION OF THE PLANThe Alliant Energy Corporation 401(k) Savings Plan (the Plan) is a qualified defined contribution plan under Section 401(k) of the Internal Revenue Code (the Code), as amended, and meets the applicable requirements of the Employee Retirement Income SecurityAct of 1974, as amended. The following brief description of the Plan is provided for general information purposes only. More completeinformation regarding the Plan is provided in the plan document and summary plan description, which have been made available to alleligible Pl