Atara Biotherapeutics, Inc.

To the shareholders and the Board of Directors of Atara Biotherapeutics, Inc.

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Atara Biotherapeutics, Inc. and subsidiaries (the "Company" or “Atara”) as of December 31, 2025 and 2024, the related consolidated statements of operations and comprehensive income (loss), stockholders’ equity (deficit), and cash flows, for each of the two years in the period ended December 31, 2025, 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, 2025 and 2024, and the results of its operations and its cash flows for each of the two years in the period ended December 31, 2025, in conformity with accounting principles generally accepted in the United States of America.

Going Concern

The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. As discussed in Note 2 to the financial statements, the Company’s negative cash flow from operations and losses from operations raises substantial doubt about its ability to continue as a going concern. Management’s plans in regard to these matters are also described in Note 2. The financial statements do not include any adjustments that might result from the outcome of this uncertainty.

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 Public Company Accounting Oversight Board (United States) (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. The Company 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 Company’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 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.

Commercialization Revenue and Deferred Revenue – Accounting for Out- License Agreements – Refer to Notes 2 and 5 to the Financial Statements

Critical Audit Matter Description

The Company has entered into certain out-license agreements with Pierre Fabre Medicament ("Pierre Fabre").

During 2021, the Company entered into a Commercialization Agreement with Pierre Fabre. Under the terms of the agreement, the Company granted Pierre Fabre a license to commercialize and distribute Ebvallo in an initial territory and became responsible for manufacturing and supplying Ebvallo to Pierre Fabre, along with related cell selection services. In 2022, the Company entered into an

Amendment Agreement to the Pierre Fabre Commercialization Agreement (the “PF Amendment No. 1”). Under the terms of the PF Amendment No. 1, Atara became entitled to an additional milestone payment in exchange for, among other things, a reduction in: (i) royalties Atara is eligible to receive, and (ii) the price mark up on supply purchased by Pierre Fabre. Additionally, Atara also agreed to extend the time period for provision of certain services to Pierre Fabre under the Pierre Fabre Commercialization Agreement. In 2023, the Company entered into an amended and restated Pierre Fabre Commercialization Agreement (the “A&R Commercialization Agreement”). Under the terms of the A&R Commercialization Agreement, the Company granted Pierre Fabre an expanded license to commercialize and distribute Ebvallo in all other countries in the world and remained responsible for manufacturing and supplying Ebvallo to Pierre Fabre, along with related cell selection services until transfer of responsibility to Pierre Fabre.

In 2024, the Company entered into an agreement with Pierre Fabre to sell certain intermediates used in the manufacture of Ebvallo for $15.5 million.

In March 2025, the Company transferred all process science services and manufacturing responsibilities to Pierre Fabre. In July 2025, the Company further amended the A&R Commercialization Agreement and completed the transfer of all development, clinical (including sponsorship of the ALLELE and tab-cel multi-cohort study) and safety activities for tab-cel to Pierre Fabre. In October 2025, Atara further amended the A&R Commercialization Agreement to transfer all regulatory activities (including sponsorship of the tab-cel BLA) to Pierre Fabre. In December 2025, the Company further amended the A&R Commercialization Agreement agreeing to reduce the milestone payment due upon BLA approval of tab-cel to $31 million in exchange for the right to receive an additional $15 million potential milestone payment upon achieving a certain commercial milestone.

The Company recognizes revenue on the commercialization agreements with Pierre Fabre as they satisfy their performance obligations and when the customer obtains control of the promised goods or services. The revenue related to the commercialization agreements with Pierre Fabre is recognized within commercialization revenue within the Consolidated Statements of Operations and Comprehensive Income (Loss). As of December 31, 2025, the Company recognized $120.8M of commercialization revenue and deferred revenue amounted to $0.7M, which is included in current liabilities.

We identified accounting for the commercialization agreements, the revenue recognized, and the estimated deferred revenue to be recognized as revenue as a critical audit matter. Given the judgments necessary to determine the accounting literature to apply to a commercialization agreement, the method to estimate and measure the progress toward the completion of the performance obligations and the estimated contractual term over which the performance obligations would be completed, auditing such judgments and estimates required extensive audit effort due to the complexity of the commercialization agreements and the high degree of auditor judgment applied when performing audit procedures and evaluating the results of those procedures.

How the Critical Audit Matter Was Addressed in the Audit

Our audit procedures related to determining the accounting literature to apply to the agreements, assessing management's method for measuring progress and evaluating management’s estimation of the contract term over which the performance obligations will be completed included the following, among others:

•

We reviewed and obtained an understanding of the Company’s revenue generating agreements and related transactions during and at the end of the year via review of internal and external presentations, news and publications, and discussions with management.

•

We evaluated the Company’s conclusions related to the accounting for contract modifications.

•

We evaluated management’s determination that the agreements are within the scope of ASC 606 - Revenue from Contracts with Customers.

•

We evaluated management's determination of the contractual term and the appropriateness of management's method to measure its progress over that term.

•

We evaluated the assumptions used in the estimates of total costs and the estimated measure of progress for recognizing revenues by:

o

Performing corroborating inquiries with the Company's project and business development managers, and comparing the assumptions used in the estimates to management's work plans, cost estimates and costs reported to date, and material rights allocated, accumulated and earned.

o

Comparing costs incurred for activities completed to date to the costs forecasted for those activities.

o

Comparing material rights accumulated and earned for activities completed to date to the fulfilment of performance obligations forecasted for those activities.

o

Testing the mathematical accuracy of management’s revenue and current and long-term deferred revenue balances based on the estimated revenue to be recognized over time.

/s/DELOITTE & TOUCHE LLP

San Francisco, California

March 16, 2026

We have served as the Company’s auditor since 2013.