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

1. Description of Plan

The following description of the 401(k) Plan as Adopted by Avidia Bank ("the Plan") (formerly the SBERA 401(k) Plan as Adopted by Avidia Bank) provides only general information. Participants should refer to the Plan agreement for a more complete description of the Plan's provisions.

General

The Plan is a defined contribution plan covering all eligible employees of Avidia Bank and subsidiaries (the "Bank" or the "Plan Sponsor"), who have attained age 18 and have completed one month of service. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA).

Principal Life Insurance Company and Delaware Charter Guarantee and Trust Company d/b/a Principal Trust Company are the Custodians and Trustees of the Plan. Prior to April 14, 2025, the Plan was part of the Savings Banks Employees Retirement Association ("SBERA") Common Collective Trust ("the Trust"). Effective April 1, 2025, the Plan Sponsor changed the name of the Plan from the SBERA 401(k) Plan as Adopted by Avidia Bank to the 401(k) Plan as Adopted by Avidia Bank and, on April 14, 2025, the Plan transferred the assets and related participant account balances from the Trust to the Custodians and Trustees.

All assets acquired under this Plan as a result of participant and Bank contributions, income and other additions will be administered, distributed, forfeited, and otherwise governed by the provisions of this Plan. The Plan assets are currently invested in various investment options offered through Principal Financial Group and its member companies ("Principal").

Contributions

Participants may contribute to the Plan a percentage of their annual compensation on a pre-tax or after-tax Roth basis as defined in the Plan, up to 75% of eligible compensation, subject to the Internal Revenue Code (IRC) limitations. Participants who have attained age 50 before the end of the Plan year are also eligible to make catch-up contributions. Participants may also contribute amounts representing distributions from other qualified plans or defined contribution plans (rollovers). Participants direct the investment of their contributions into various investment options offered by the Plan. The Bank makes a safe harbor matching contribution equal to 100% of eligible participant deferrals, up to 5% of each participant's eligible compensation contributed to the Plan.

Participant Accounts

Each participant's account is credited with the participant's contributions and Bank matching contributions and Plan earnings. Participant accounts are charged with an allocation of administrative expenses that are paid by the Plan. Allocations are based on participant earnings, account balances, or specific participant transactions, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant's vested account.

Vesting

Participants are 100% vested in all contributions plus actual earnings thereon.

401(k) PLAN AS ADOPTED BY AVIDIA BANK

Notes to Financial Statements (continued)

December 31, 2025 and 2024

1. Description of Plan (continued)

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. Notes are required to be repaid within 5 years unless the note is to be used for the purchase of a primary residence and such loan term shall be a period consistent with commercial home loan practices. Participants may have up to two loans outstanding at any time. The notes are secured by the balance in the participant's account and bear interest at a rate based on the rates available for similar loans from commercial lending institutions. The loan administrator periodically examines the rates such lenders are using. Once a loan is granted, the interest rate on that loan will not change. Principal and interest is paid ratably through payroll deductions if available.

Payment of Benefits

Upon termination of service due to death, disability, normal retirement, or attaining age 59½, a participant may elect to receive either a lump sum amount equal to the value of the participant's vested interest in their account, annual installments, or defer distribution until a later date. If the vested portion of a participant's account balance is $1,000 or less, and the participant does not provide alternative instructions to the Plan Sponsor, this amount is paid as a lump sum distribution as soon as possible following termination, retirement, disability, or to the beneficiary following death. Participants may request a benefit payment in the case of financial hardship, subject to certain limitations as defined by the Plan.

Plan Termination

Although it has not expressed any intent to do so, the Bank has the right under the Plan to discontinue its contributions at any time and to terminate the Plan, subject to the provisions of ERISA. In the event of Plan termination, the net assets of the Plan would be allocated as prescribed by ERISA and its related regulations.

2. Summary of Accounting Policies

3. Fair Value Measurements

The framework for measuring fair value provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). Valuation techniques maximize the use of relevant observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy under the Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") 820, Fair Value Measurement, are described as follows:

Level 1 - Valuation is based on quoted prices in active markets for identical assets or liabilities. Valuations are obtained from readily available pricing sources for market transactions involving identical assets or liabilities.

Level 2 - Valuation is based on observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 - Valuation is based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Level 3 assets and liabilities include financial instruments whose value is determined using unobservable inputs to pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.

In certain cases, inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, an investment's level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. The Plan's assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the investment.

The following is a description of the valuation methodologies used for assets measured at fair value.

Pooled separate accounts ("PSA"): Valued daily based on the market value of the underlying net assets in each separate account. The majority of the underlying net assets have observable Level 1 and/or 2 quoted pricing inputs which are used to determine the unit value of the PSA which is not publicly quoted. These PSAs are classified as Level 1. The redemption frequency of each of these PSAs is daily, and there are no redemption restrictions.

The following table sets forth by level, within the fair value hierarchy, the Plan's assets at fair value as of December 31, 2025:

The following table sets forth by level, within the fair value hierarchy, the Trust's assets at fair value as of December 31, 2024:

401(k) PLAN AS ADOPTED BY AVIDIA BANK

Notes to Financial Statements (continued)

December 31, 2025 and 2024

3. Fair Value Measurements (continued)

Investments Measured Using the NAV per Share Practical Expedient

Effective April 14, 2025, the Company transferred the assets and related participant account balances from the Trust to the 401(k) Plan as Adopted by Avidia Bank; therefore, the Plan's investments were no longer in the Trust as of December 31, 2025. As of December 31, 2024, all of the Plan's investments were in the Trust, which was established for the investment of assets of the Plan and several other member bank sponsored retirement plans. Each participating retirement plan has a divided interest in the Trust. The assets of the Trust are held by several custodians. The Trust allows for daily redemptions. The Plan does not have any unfunded commitments. The value of the Plan's interest in the Trust is based on the beginning of year value of the Plan's interest in the Trust plus actual contributions and allocated investment income less actual distributions and allocated administrative expenses plus the Plan's portion of notes receivable from participants held as of the Plan year-end. At December 31, 2024, the Plan's interest in the Trust was approximately 2.29%. Investment income and administrative expenses relating to the Trust are allocated to the individual plans based upon average monthly balances invested by each plan.

5. Group Annuity Contract

The Plan has entered into a fully benefit-responsive group annuity contract with Principal Life Insurance Company. The traditional investment contract is reflected in the financial statements at contract value as reported to the Plan by Principal Life Insurance Company. There are no reserves against contract value for credit risk of the contract issuer or otherwise.

The crediting interest rate is based on the rate in effect on the date of the deposit and is credited annually on the anniversary date of the deposit. The guaranteed investment contract does not permit the insurance company to terminate the agreement except under certain circumstances outlined in the contract.

This contract meets the fully benefit-responsive investment contract criteria and therefore is reported at contract value. Contract value is the relevant measure for a fully benefit-responsive investment contract because this is the amount received by participants if they were to initiate permitted transactions under the terms of the Plan. Contract value, as reported to the Plan by Principal, represents contributions made under the contract, plus earnings, less participant withdrawals, and administrative expenses. Participants may ordinarily direct the withdrawal or transfer of all or a portion of their investment at contract value.

The Plan's ability to receive amounts due is dependent on the issuer's ability to meet its financial obligations. The issuer's ability to meet its contractual obligations may be affected by future economic and regulatory developments.

6. Tax Status

The Plan adopted the Principal Financial Group Pre-Approved Document for Savings Plans, which received an opinion letter from the Internal Revenue Service ("IRS") dated June 30, 2020, stating that the written form of the underlying Plan document is qualified under Section 401(a) of the IRC. Although the Plan has been amended since receiving the opinion letter, the Plan Administrator and the Plan's tax counsel believe that the Plan is designed, and is currently being operated, in compliance with the applicable requirements of the IRC and, therefore, believe that the Plan is qualified, and the related trust is tax-exempt.

U.S. GAAP requires Plan management to evaluate tax positions taken by the Plan and recognize a tax liability if the Plan has taken an uncertain position that more likely than not would not be sustained upon examination by the IRS or the Department of Labor. The Plan Administrator has analyzed the tax positions taken by the Plan, and has concluded that as of December 31, 2025 and 2024, there are no uncertain tax positions taken or expected to be taken that would require recognition of a liability or disclosure in the financial statements. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress.

7. Party-In-Interest Transactions

The Plan's record keeper, Trustees, and Custodians, as well as the Company and Plan participants, and the auditor of the Plan's financial statements, are each a "party-in-interest" to the Plan as defined by ERISA. Certain administrative functions are performed by employees and officers of the Bank for which no compensation was paid from the Plan. Certain Plan investments are in shares of Avidia Bancorp, Inc. common stock and contracts issued by Principal. The Plan also issues notes receivable from participants. For the Plan year ended December 31, 2025, fees paid to the Custodians amounted to $10,934. Expenses paid by the Plan to the Plan's record keeper, Trustees, and Custodians represent party-in-interest transactions. As of December 31, 2025, the Plan held 554,198 shares of Avidia Bancorp, Inc. common stock.

8. Risks and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks such as interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants' account balances and the amounts reported in the statements of net assets available for benefits.

9. Subsequent Events

For purposes of accrual or disclosure in these financial statements, the Company has evaluated subsequent events through the date of issuance of these financial statements.

** Participant-directed investments for which historical cost information is not required to be presented.