Annual Report of Employee Stock Purchase/Savings Plan (Form 11-K)

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 11-K

(Mark One)

FOR THE FISCAL YEAR ENDED DECEMBER 31, 2025

or

FOR THE TRANSITION PERIOD FROM TO

Commission file number 1-3701

THE INVESTMENT AND EMPLOYEE STOCK

OWNERSHIP PLAN OF

AVISTA CORPORATION

(Full Title of the Plan)

AVISTA CORPORATION

1411 East Mission Avenue

Spokane, Washington 99202-2600

(Name of issuer of the securities held pursuant to the plan

and the address of its principal executive office)

Table of Contents

THE INVESTMENT AND EMPLOYEE STOCK OWNERSHIP PLAN

OF AVISTA CORPORATION

FINANCIAL STATEMENTS AND

SUPPLEMENTAL INFORMATION

YEARS ENDED DECEMBER 31, 2025 AND 2024

2

Table of Contents

TABLE OF CONTENTS

3

Table of Contents

Report of Independent Registered Public Accounting Firm

The Compensation and Organization Committee and

Benefit Plans Administration Committee and participants of

The Investment and Employee Stock Ownership Plan

of Avista Corporation

Opinion on the Financial Statements

We have audited the accompanying statements of net assets available for benefits of The Investment and Employee Stock Ownership Plan of Avista Corporation (the "Plan") as of December 31, 2025 and 2024, the related statements of changes in net assets available for benefits for the years then ended, and the related notes (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2025 and 2024, and the changes in net assets available for benefits for the years then ended in conformity with accounting principles generally accepted in the United States of America.

Basis for Opinion

These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on the Plan's financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) ("PCAOB") and are required to be independent with respect to the Plan 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 audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Plan is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Plan's internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures to respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

Opinion on the Supplemental Information

The supplemental information included in Schedule H, line 4(i) - schedule of assets (held at end of year) as of December 31, 2025, has been subjected to audit procedures performed in conjunction with the audit of the Plan's financial statements. The supplemental information is the responsibility of the Plan's management. Our audit procedures included determining whether the supplemental information reconciles to the financial statements or the underlying accounting and other records, as applicable, and performing procedures to test the completeness and accuracy of the information presented in the supplemental information. In forming our opinion on the supplemental information in the accompanying schedule, we evaluated whether the supplemental information, including its form and content, is presented in conformity with Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. In our opinion, the supplemental information in the accompanying schedule is fairly stated, in all material respects, in relation to the financial statements as a whole.

/s/ Baker Tilly US, LLP

Spokane, Washington

June 25, 2026

We have served as the Plan's auditor since 2023.

4

Table of Contents

THE INVESTMENT AND EMPLOYEE STOCK OWNERSHIP PLAN

OF AVISTA CORPORATION

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS

DECEMBER 31, 2025 AND 2024

See accompanying Notes to Financial Statements.

5

Table of Contents

THE INVESTMENT AND EMPLOYEE STOCK OWNERSHIP PLAN

OF AVISTA CORPORATION

STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS

YEARS ENDED DECEMBER 31, 2025 AND 2024

See accompanying Notes to Financial Statements.

6

Table of Contents

NOTE 1. DESCRIPTION OF THE PLAN

The following description of The Investment and Employee Stock Ownership Plan of Avista Corporation (the Plan) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan's provisions.

General

Effective January 1, 1984, Avista Corporation (Corporation, Company or Avista) established an Employee Investment Plan under Section 401(k) of the Internal Revenue Code (IRC). The Plan, which was restated effective January 1, 2016, and most recently amended effective December 16, 2024, is a defined contribution plan which is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA) and all statutory revisions thereto. The purpose of the Plan, in which participation is voluntary, is to encourage employees to systematically save a portion of their compensation and to supplement their savings with contributions from Avista. All employees of Avista are eligible to participate in the Plan after their first pay period following employment. Students, leased employees, and collectively bargained employees (other than collectively bargained employees whose employment is subject to the terms of a collective bargaining agreement which provides for participation in the Plan) are ineligible to participate in the Plan.

Contributions

Plan participants may make contributions during any payroll period for which they receive earnings as eligible employees in an amount at least equal to 1% of their earnings. A participating employee's annual before-tax contribution was subject to IRC limitations of $23,500 in 2025 and $23,000 in 2024. Participants who have attained age 50 before the end of the Plan year are eligible to make catch-up contributions. Participants may also contribute amounts representing distributions from other qualified defined benefit or defined contribution plans, subject to IRC limits. Employee contributions represent tax-deferred compensation and Roth 401(k) after tax compensation and may be invested in the employee's choice of various fund options (each with a different investment objective and risk) in the combination specified by the employee. Employee contributions are made by payroll deduction and transferred to the Plan Trustee as soon as practicable following the payroll period in which such amounts are withheld.

Plan participants hired prior to April 1, 2022 are automatically enrolled in the Plan upon eligibility at a 3% deferral rate, with an automatic increase of 1% each year up to 15%.

Plan participants hired on or after April 1, 2022 are automatically enrolled in the Plan upon eligibility at a 6% deferral rate, with an automatic increase of 1% each year up to 15%.

Participants can opt out of the Plan at any time. Participants can change their deferral rate at any time.

Plan participants may transfer balances from other qualified defined benefit or defined contribution plans, and certain eligible retirement plans and accounts to the Plan.

Avista has an obligation to the trust fund for an amount equal to a percentage of employee contributions determined by the hire date of the employee.

All non-collectively bargained employees and Local 659 employees hired prior to January 1, 2006, and Local 77 employees hired prior to January 1, 2011, receive a matching contribution of 75% of employee contributions that does not exceed 6% of the employee's salary.

All non-collectively bargained employees and Local 659 employees hired on or after January 1, 2006, and Local 77 employees hired on or after January 1, 2011, receive a matching contribution of 100% of employee contributions that does not exceed 6% of the employee's salary.

7

Table of Contents

Further, all non-collectively bargained employees hired on or after January 1, 2014, Local 659 employees hired on or after April 1, 2014, Local 77 employees hired on or after April 1, 2017 as a Distribution Dispatcher or Gas Controller from outside Avista or who is ineligible to participate in the Retirement Plan for Employees of Avista Corporation, Local 77 members hired on or after January 1, 2024, and any participant who elected to waive participation in the Retirement Plan for Employees of Avista Corporation as of July 1, 2024, receive an additional non-elective employer contribution based on the employee's age. The table below illustrates the non-elective contribution rate assigned to the established age groups.

Local 77 members hired on or after January 1, 2024, or who waived participation in the Retirement Plan for Employees of Avista Corporation who are not Distribution Operators, Gas Controllers, or non-collectively bargained employees are also eligible for an additional Employer non-elective contribution equal to 5% of eligible compensation. Remaining Local 77 employees are eligible for the additional non-elective contribution equal to 5% of eligible compensation as of December 16, 2024.

The Company matching contributions are made in the form of cash that is invested as directed by participants from among the investment options offered under the Plan.

Any employees who transfer or have transferred from a Local 77 employee directly to non-Local 77 employee on or after January 1, 2014, other than those Local 77 employees hired on or after April 1, 2017 as a Distribution Dispatcher or Gas Controller from outside Avista or who is ineligible to participate in the Retirement Plan for Employees of Avista Corporation, are not eligible for the additional non-elective employer contributions.

Participant Accounts

Each participant's account is credited with the participant's contribution and allocations of (a) the Company's contribution and (b) Plan earnings or losses, and charged with an allocation of administrative expenses. Allocations are based on participant earnings or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant's vested account.

Vesting

Participant contributions are 100% vested at all times. Participants vest 100% in the Company matching contribution after one year of service or upon death, disability or reaching normal retirement age. Participants vest 100% in the non-elective employer contribution after three years of service or upon death, disability or reaching normal retirement age.

Notes Receivable from Participants

Participants may borrow from their fund accounts a minimum of $1,000 up to a maximum equal to the lesser of $50,000 or 50% of their vested account balance. Principal and interest is paid ratably through payroll deductions. The notes are secured by the balance in the participant's account and bear interest at a rate of prime rate plus 1%. The maximum term of a general loan is five years, and the maximum term of a primary residence loan is 10 years. Interest rates ranged from 4.25% to 9.50% at December 31, 2025, for loans maturing through 2034.

Payment of Benefits

Distributions to participants are permitted for termination, retirement, death, disability, or financial hardship. A participant with a financial hardship which imposes an immediate and heavy financial need that cannot be reasonably met by other sources may withdraw a portion of their account balance subject to provisions of the Plan. Distributions due to termination shall commence as soon as administratively feasible following the date a participant terminates employment. Distributions may be made in a lump sum, partial lump sum, equal annual installments over a period not to exceed 3 years, or monthly installments over not more than 15 years. If the vested amount is less than $1,000, the account is paid in a lump-sum payment to the participant within a reasonable time frame. If the vested amount is more than $1,000, the participant must consent to the distribution before it may be made.

8

Table of Contents

9

Table of Contents

10

Table of Contents

11

Table of Contents

12

Table of Contents

THE INVESTMENT AND EMPLOYEE STOCK OWNERSHIP PLAN

OF AVISTA CORPORATION

E.I.N. 91-0462470 PLAN NO. 003

SCHEDULE H, LINE 4i -- SCHEDULE OF ASSETS (HELD AT END OF YEAR)

DECEMBER 31, 2025

* Designates party-in-interest.

** Cost omitted for participant-directed investments.

13

Table of Contents

EXHIBIT INDEX

14

Table of Contents

SIGNATURES

The Plan. Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

15