Conversion and Change in Corporate Form

Effective July 31, 2025, Assabet Valley Bancorp, the former mutual holding company of Avidia Bank and the predecessor to Avidia Bancorp, Inc., consummated its mutual to stock conversion and the Company consummated its related stock offering. In the offering, the Company sold 19,176,250 shares of common stock at a per share price of $10.00, including 1,606,100 shares of common stock purchased by the Bank's employee stock ownership plan, for net offering proceeds of approximately $185.8 million. Additionally, the Company donated $1.0 million of cash and 900,000 shares of common stock to the Avidia Bank Charitable Foundation (the "Foundation"). A total of 20,076,250 shares of common stock of the Company were issued and outstanding immediately after the donation to the Foundation. The purchase of the common stock by the ESOP was financed by a loan from the Company.

In connection with the conversion, the Company and the Bank established liquidation accounts in an amount equal to Assabet Valley Bancorp’s total equity as reflected in the latest consolidated balance sheets contained in the final offering prospectus for the conversion. The liquidation accounts will be maintained for the benefit of eligible account holders (as defined in the Plan) and supplemental eligible account holders (as defined in the Plan) (collectively, “eligible depositors”) who continue to maintain their deposit accounts in the Bank after the conversion. In the event of a complete liquidation of either (i) the Bank or (ii) the Bank and the Company (and only in such events), eligible depositors who continue to maintain their deposit accounts will be entitled to receive a distribution from the liquidation accounts before any distribution may be made with respect to the common stock of the Company.

The Company may not declare or pay a cash dividend if the effect thereof would cause its equity to be reduced below either the amount required for the liquidation accounts or the regulatory capital requirements imposed by its respective bank regulators.

Reclassification

Certain items in prior consolidated financial statements have been reclassified to conform to the current presentation.

Segment Information

The Company's reportable segment is determined by the Chief Financial Officer, who is the designated chief operating decision maker, based upon information provided about the Company's products and services offered, primarily banking operations. The segment is also distinguished by the level of information provided by the chief operating decision maker, who uses such information to review performance of various components of the business, which are then aggregated if operating performance, products/services, and customers are similar. The chief operating decision maker will evaluate the

financial performance of the Company's business components such as by evaluating revenue streams, significant expenses, and budget to actual results in assessing the Company's segment and in the determination of allocating resources. The chief operating decision maker uses revenue streams to evaluate product pricing and significant expenses to assess performance and evaluate return on assets. The chief operating decision maker uses consolidated net income to benchmark the Company against its competitors. The benchmarking analysis coupled with monitoring of budget to actual results are used in assessing performance and in establishing compensation. Loans, investments, and deposit product service fees provide the revenues in the banking operation. Interest expense, credit loss expense, and salaries and employee benefits, as reported on the consolidated statements of operations, provide the significant expenses in the banking operation. All operations are domestic.

Accounting policies for segments are the same as those described herein. Segment performance is evaluated using consolidated net income. The measure of segment assets is reported on the consolidated balance sheets as total consolidated assets. Noncash items, such as depreciation and amortization, as well as expenditures for premises and equipment, are reported on the consolidated statements of cash flows.

Recently Adopted Accounting Standards

In December 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2023-09, Income Taxes (Topic 740) - Improvements to Income Tax Disclosures. The ASU provides more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information, such as requiring the disclosure of specific categories in the rate reconciliation and the disaggregation of income tax expense and income taxes paid by federal, state, and foreign taxes. This ASU was adopted December 31, 2025, and it did not have a material impact on the Company’s consolidated financial statements.

Future Accounting Pronouncements

In November 2024, the FASB issued ASU No. 2024-03, Income Statement - Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. This ASU will require public companies to disclose, in the notes to financial statements, specified information about certain costs and expenses at each interim and annual reporting period. The amendments in this ASU are effective for fiscal years beginning after December 15, 2026, and interim reporting periods within annual reporting periods beginning after December 15, 2027, with early adoption permitted. The Company does not expect this ASU to have a material impact on the Company's consolidated financial statements.

In November 2025, the FASB issued ASU 2025-08, Financial Instruments - Credit Losses (Topic 326): Purchased Loans. This ASU revises Topic 326 to simplify and improve the accounting for acquired financial assets. The update expands the application of the gross-up approach to include purchased seasoned loans, eliminating the complexity and inconsistency created by having separate models for purchased credit deteriorated ("PCD") and non-PCD assets. Under the new guidance, the initial allowance for credit losses is added to the amortized cost basis rather than recorded as a Day 1 provision expense.

The amendments in this update are effective for all entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. Early adoption is permitted. The Company does not expect this ASU to have a material impact on the Company's consolidated financial statements.

In November 2025, the FASB issued ASU 2025-09, Derivatives and Hedging (Topic 815): Hedge Accounting Improvements. This ASU introduces clarifications to Topic 815 building on improvements from ASU 2017‑12, and addresses challenges arising from the global reference rate reform (i.e., the LIBOR transition). The new guidance aims to reduce complexity in applying hedge accounting to transactions tied to an entity’s risk management activities and promotes consistency in accounting for forecasted transactions, interest rate flexibility, and nonfinancial components. The update expands eligibility for hedge accounting by allowing groups of forecasted transactions with similar risk exposures, provides guidance for hedging interest payments on debt with selectable interest rate indexes, clarifies hedging of specified components of nonfinancial assets, and eases restrictions related to net written options and certain compound derivatives. It also resolves presentation mismatches for certain foreign currency hedging relationships. The amendments in this update are effective for all entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. Early adoption is permitted. The Company does not expect this ASU to have a material impact on the Company's consolidated financial statements.