DEEP FISSION, INC. (0001918102) (Filer)

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 20, 2026

Deep Fission, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (707) 400-0778

N/A

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Item 7.01 – Regulation FD Disclosure

Press Release

On October 20, 2026, Deep Fission, Inc. (the “Company”) issued a press release announcing that it had entered into a Master Energy Purchase Agreement (the “Agreement”) with the Great Plains Development Authority relating to a planned commercial nuclear power project at the Great Plains Industrial Park in Parsons, Kansas. The Agreement is subject to regulatory approvals and other conditions to commercial operation, and electricity purchases will depend on actual tenant demand, with no minimum purchase obligation. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K (this “Current Report”) and is incorporated herein by reference.

Investor Presentation

On October 20, 2026, the Company held an investor update call. A copy of the presentation used in connection with the call is furnished as Exhibit 99.2 to this Current Report and is incorporated herein by reference.

The information in this Item 7.01, including Exhibits 99.1 and 99.2, is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly provided by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.