Keros Therapeutics Inc

To the stockholders and the Board of Directors of Keros Therapeutics, Inc.

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Keros Therapeutics, Inc. and subsidiaries (the "Company") as of December 31, 2024 and 2023, the related consolidated statements of operations, stockholders' equity, and cash flows, for each of the three years in the period ended December 31, 2024, and the related notes (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2024 and 2023, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2024, in conformity with accounting principles generally accepted in the United States of America.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of December 31, 2024, based on criteria established in Internal Control — Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission and our report dated February 26, 2025, expressed an unqualified opinion on the Company's internal control over financial reporting.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company's financial statements based on our audits. 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 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. 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 that 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.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current-period audit of the financial statements that was communicated or required to be communicated to the audit committee and that (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of critical audit matters does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Accrued and Prepaid Research and Development and Manufacturing Expenses — Refer to Notes 2, 4 and 6 to the financial statements

Critical Audit Matter Description

As disclosed in Note 2 to the financial statements, the Company records accrued and prepaid research and development expenses for external clinical trial costs and manufacturing activities based on estimates of the progress to completion of specific tasks within individual contract research and contract manufacturing arrangements. Estimates of expenses incurred are determined by reviewing information provided to the Company by its service providers and through discussions with both internal personnel and external service providers as to the status of specific tasks within arrangements. Expenses incurred in excess of amounts invoiced are recorded as accrued expenses. Payments made in excess of expenses incurred are recorded as prepaid costs. As of December 31, 2024, the Company has recorded accrued external research, development, and manufacturing costs of $9.4 million and prepaid research, development and manufacturing costs of $21.3 million.

We identified auditing the estimates of the progress to completion of specific tasks performed by contract research and contract manufacturing service providers as a critical audit matter due to the (i) the level of judgment required by management and the volume of such estimates made by management and (ii) the high degree of auditor judgment, subjectivity, and an increased extent of effort in performing procedures to evaluate the reasonableness of management’s estimates of progress to completion.

How the Critical Audit Matter Was Addressed in the Audit

Our audit procedures related to accrued and prepaid external research and development expenses and manufacturing costs included the following, among others:

•We tested the design and effectiveness of relevant controls over the estimation of accrued and prepaid research and development expenses and manufacturing costs.

•For a sample of contracts with service providers performing research and development, and manufacturing activities, we performed the following:

◦Evaluated the appropriateness of the method used by management to develop its estimates of progress to completion of specific tasks.

◦Tested the completeness and accuracy of the underlying data used in the estimates of progress to completion through inspection of the terms of contracts and statements of work between the Company and its service providers and testing of actual billed expenses under the contracts.

◦Performed corroborating inquiries with Company personnel responsible for overseeing the activities performed by the Company’s contract research and contract manufacturing service providers, which may include the service providers’ estimate of completed tasks or progress of completion of certain tasks within the arrangement.

/s/Deloitte & Touche LLP

Boston, Massachusetts

February 26, 2025

We have served as the Company's auditor since 2019.