Atara Biotherapeutics, Inc. Income Taxes Disclosure

We adopted ASU 2023-09 "Income Taxes (Topic 740): Improvements To Income Tax Disclosures" on a prospective basis beginning with the year ended December 31, 2025. The following table presents required disclosure pursuant to ASU 2023-09 and reconciles the U.S. federal statutory tax amount and rate to our actual global effective amount and rate for the year ended December 31, 2025:

Deferred tax assets and liabilities reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and (b) operating loss and tax credit carryforwards. Significant components of our deferred tax assets and liabilities were as follows for each of the dates presented:

We recognize deferred income taxes for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes, as well as for tax attribute carryforwards. We regularly evaluate the positive and negative evidence in determining the realizability of our deferred tax assets. Based upon the weight of available evidence, which includes our historical operating performance and reported cumulative net losses since inception, we maintained a full valuation allowance on the net deferred tax assets as of December 31, 2025 and December 31, 2024. We intend to maintain a full valuation allowance on our deferred tax assets until sufficient positive evidence exists to support reversal of the valuation allowance. The valuation allowance decreased by $13.4 million for the year ended December 31, 2025 and increased by $106.6 million for the year ended December 31, 2024.

As of December 31, 2025, we reported U.S. federal and state NOLs of approximately $1,361.4 million and $72.7 million,

respectively. Our federal NOLs generated prior to 2018 aggregating to $15.3 million will continue to be governed by the NOL tax rules as they existed prior to the adoption of the Tax Act, which means that generally they will expire 20 years after they were generated if not used prior thereto. Many states have similar laws, and our state NOLs will begin to expire in 2030. Accordingly, these federal and state NOLs could expire unused and be unavailable to offset future income tax liabilities. Under the Tax Act, as modified by the CARES Act, federal NOLs incurred in 2018 and in future years may be carried forward indefinitely, but the utilization of such federal NOLs is limited to 80% of current year taxable income. Not all states conform to the Tax Act or CARES Act and other states have varying conformity to the Tax Act or CARES Act.

As of December 31, 2025, we generated federal research and development tax credit carryforwards of $1.1 million, which will begin to expire in 2044. As of December 31, 2025, we had state credit carryforwards of $46.1 million available to reduce future tax liabilities, which do not expire.

On July 4, 2025, the One Big Beautiful Bill (“OBBBA”) was signed into law. The OBBBA includes a broad range of U.S. tax reform measures, including, among other provisions, the immediate expensing of U.S. research and development expenditures. In accordance with ASC 740, the Company has recognized the effects of the new tax law in the period of enactment. As the Company maintains a full valuation allowance on its U.S. deferred tax assets, the legislation does not have a material impact on its consolidated financial statements.

Under Section 382 of the Internal Revenue Code of 1986, as amended (the “Code”), our ability to utilize net operating loss carryforwards or other tax attributes in any taxable year may be limited if we have experienced an “ownership change.” Generally, a Section 382 “ownership change” occurs if one or more stockholders or groups of stockholders who owns at least 5% of a corporation’s stock increases its ownership by more than 50 percentage points over its lowest ownership percentage within a specified testing period. Similar rules may apply under state tax laws.

We have completed a Section 382 study of transactions in our stock through December 31, 2024. The study concluded that we have experienced ownership changes since inception and that our utilization of net operating loss carryforwards and tax credits will be subject to annual limitations. The annual limitations did result in the expiration of tax attribute carryforwards prior to utilization. As of December 31, 2025, no additional ownership change occurred.

We currently have a full valuation allowance against its U.S. net deferred tax assets, which would impact the timing of the effective tax rate benefit should any uncertain tax position be favorably settled in the future.

Our policy is to account for interest and penalties related to uncertain tax positions as a component of the income tax provision. The Company has not accrued interest and penalties as of December 31, 2025 due to available tax losses.

Our significant jurisdictions are the U.S. federal jurisdiction and the California state jurisdiction. All of our tax years remain open to examination by the U.S. federal and California tax authorities.