Change in Certifying Accountants (Form 8-K)

Item 4.01 Changes in Registrant's Certifying Accountant.

On February 27, 2026, the Audit Committee of the Board of Directors (the "Audit Committee") of Deep Fission, Inc. (the "Company") approved the engagement of Grant Thornton LLP ("Grant Thornton") as the Company's independent registered public accounting firm to audit the Company's consolidated financial statements for the fiscal years ended December 31, 2024 and 2025. Accordingly, dbbmckennon ("dbbmckennon"), the Company's independent registered public accounting firm since September 5, 2025, was informed that it would be replaced as the Company's independent registered public accounting firm effective February 27, 2026.

The reports of dbbmckennon on the Company's consolidated financial statements as of and for the fiscal years ended December 31, 2024 and 2023 did not contain an adverse opinion or a disclaimer of opinion, nor were such reports qualified or modified as to uncertainty, audit scope or accounting principles, except that such reports included an explanatory paragraph regarding substantial doubt about the Company's ability to continue as a going concern.

During the fiscal years ended December 31, 2024 and 2023 and the subsequent interim period through February 27, 2026, there were no (i) disagreements (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions thereto) with dbbmckennon on any matter of accounting principles or practices, financial statement disclosure or auditing scope or procedure, which disagreements, if not resolved to dbbmckennon's satisfaction, would have caused dbbmckennon to make reference to the subject matter thereof in connection with its reports, or (ii) reportable events (as defined in Item 304(a)(1)(v) of Regulation S-K and the related instructions thereto), other than, as previously disclosed in the Company's Quarterly Report on Form 10-Q for the quarter ended September 30, 2025, the Company identified a material weakness in internal control over financial reporting related to the design and operating effectiveness of controls over the Company's financial reporting process, including the formalization and documentation of controls and management review procedures commensurate with a public reporting company. The Audit Committee discussed the material weakness with dbbmckennon and has authorized dbbmckennon to respond fully to inquiries of Grant Thornton concerning such material weakness. Such material weakness did not result in any restatement of the Company's financial statements and did not give rise to any disagreement between the Company and dbbmckennon.

The Company has provided dbbmckennon with a copy of the foregoing disclosures and has requested that dbbmckennon furnish the Company with a letter addressed to the Securities and Exchange Commission stating whether it agrees with the statements made herein and, if not, stating the respects in which it does not agree. A copy of dbbmckennon's letter is filed as Exhibit 16.1 to this Current Report on Form 8-K.

During the fiscal years ended December 31, 2024 and 2023 and the subsequent interim period through February 27, 2026, neither the Company nor anyone on its behalf consulted with Grant Thornton regarding (i) the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the Company's financial statements, and neither a written report nor oral advice was provided to the Company by Grant Thornton that Grant Thornton concluded was an important factor considered by the Company in reaching a decision as to any accounting, auditing or financial reporting issue, or (ii) any matter that was either the subject of a disagreement (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions thereto) or a reportable event (as defined in Item 304(a)(1)(v) of Regulation S-K and the related instructions thereto).