Boundless Bio, Inc. Income Taxes Disclosure

Income Tax Expense

For the years ended December 31, 2025 and 2024, the Company’s pre-tax loss was entirely domestic. The Company adopted ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, effective January 1, 2025. See Note 1 for additional information regarding the adoption of this standard.

The majority of our domestic operations are located in the state of California. The Company paid no federal, state, or foreign income taxes, net of refunds received, during the years ended December 31, 2025 and 2024.

As of December 31, 2025, the Company has not recorded any current or deferred federal, state, or foreign income tax expense or benefit due to its full valuation allowance against deferred tax assets.

Deferred Tax Assets and Liabilities

Valuation Allowance

Net Operating Loss and Credit Carryforwards

The Company has established a full valuation allowance against its net deferred tax assets due to uncertainty regarding realization. In assessing the need for a valuation allowance, management considered the Company’s history of cumulative pre-tax losses, the lack of sufficient taxable income in prior carryback periods, the limited existence of taxable temporary differences, and the uncertainty surrounding future taxable income.

During 2025 and 2024, total deferred tax assets, net of deferred tax liabilities, increased by approximately $16.3 million and $20.5 million, respectively. Due to the full valuation allowance position, the Company’s valuation allowance increased by a corresponding amount in each period.

Federal net operating loss carryforwards are subject to potential limitations under Section 382 of the Internal Revenue Code of 1986, as amended (“IRC”). Certain state NOL carryforwards begin to expire in 2038. Federal research tax credits begin to expire in 2040, while unused state credits carry forward indefinitely.

Section 382 Limitations

Pursuant to IRC Sections 382 and 383, the Company’s ability to use its NOL and research tax credit carryforwards to offset future taxable income may be limited if the Company experiences a cumulative change in ownership of more than 50% within a three-year testing period. The Company has not completed an ownership change analysis pursuant to IRC Section 382. If ownership changes within the meaning of IRC Section 382 are identified as having occurred, the amount of NOL and research tax carryforwards available to offset future taxable income and income tax liabilities in future years may be significantly reduced, restricted, or eliminated. The Company has also not performed a formal research and development credit study with respect to these credits. As such, the amount of such credits may be reduced in the future should the Company complete such a study. Moreover, deferred tax assets associated with such NOLs and research tax credits could be significantly reduced upon realization of an ownership change within the meaning of IRC Section 382.

Recent Tax Legislation

On July 4, 2025, the reconciliation bill commonly referred to as the One Big Beautiful Bill Act (“OBBBA”) was signed into law in the United States. The OBBBA includes a broad range of tax reform provisions affecting U.S. corporate income taxation. Certain provisions became effective beginning in 2025, including an elective deduction for domestic research and development expenditures, reinstatement of 100% first-year bonus depreciation, and repeal of the fiscal year-end requirement for certain non-U.S. corporations. Other provisions of the OBBBA will become effective in 2026 and subsequent years, including a more favorable tax rate applicable to Foreign-Derived Deduction Eligible Income and income from non-U.S. subsidiaries (Net CFC Tested Income).

Due to the Company’s full valuation allowance on deferred tax assets, the enactment of the OBBBA did not have a material impact on the Company’s financial statements for the year ended December 31, 2025, other than the reclassification of certain deferred tax assets and liabilities.

There are no accruals for interest or tax penalties in the accompanying balance sheets, and the Company has not recognized any such interest or tax penalties in the accompanying statements of operations and comprehensive loss. Although it is not currently under a tax examination, all of the Company’s tax years remain open to audit in all of the tax jurisdictions in which it operates due to the Company’s net operating losses carryforwards.

Uncertain Tax Benefits

The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. As of December 31, 2025 and 2024, the Company had no accrued interest or penalties.

The Company is not currently under examination by any taxing authority. Due to the existence of net operating loss carryforwards, all tax years remain open to examination in the jurisdictions in which the Company operates.