DEEP FISSION, INC.

As filed with the Securities and Exchange Commission on September 19, 2025.

Registration Number 333-

**UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

**FORMS-1

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933

Deep Fission, Inc.

(Exact name of registrant as specified in its charter)

2831 Garber Street

Berkeley, California 94705

‪**(707) 400-0778

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

**Elizabeth Muller

Chief Executive Officer

2831 Garber Street

Berkeley, California 94705

‪**(707) 400-0778**

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Gordon Ho

**John T. McKenna

Cooley LLP

3175 Hanover Street

Palo Alto, California 94304

(650) 843-5000

From time to time after this registration statement is declared effective.

(Approximate date of commencement of proposed sale to the public)

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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 7(a)(2)(B) of the Exchange Act.☐

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until this Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. The selling stockholders may not sell these securities pursuant to this prospectus until the registration statement filed with the Securities and Exchange Commission becomes effective. This preliminary prospectus is not an offer to sell these securities and is not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED SEPTEMBER 19, 2025

PRELIMINARY PROSPECTUS

Up to 50,874,089 Shares of Common Stock

Up to 586,666 Shares of Common Stock Issuable Upon Exercise of Warrants

This prospectus relates to the offering and resale by the selling stockholders identified herein of up to 51,460,755 shares of common stock, par value $0.0001 per share, of Deep Fission, Inc. (“Deep Fission” or the “Company”), consisting of:

The selling stockholders may offer, sell or distribute all or a portion of the securities hereby registered publicly or through private transactions at prevailing market prices or at negotiated prices. We will not receive any proceeds from the sale of the shares of common stock by the selling stockholders, except with respect to amounts that may be received by us upon exercise of the Placement Agent Warrants. For a list of the selling stockholders, see the section titled “Selling Stockholders.” We have borne and will continue to bear the costs relating to the registration of these shares. We will bear all costs, expenses and fees in connection with the registration of these securities, including with regard to compliance with state securities or “blue sky” laws. The selling stockholders will bear all commissions and discounts, if any, attributable to their sale of shares of common stock. See the section titled “Plan of Distribution.”

There is not currently, and there has never been, any established public trading market for any of our securities. The common stock is not currently eligible for trading on any national securities exchange, including The Nasdaq Stock Market, LLC, or any over-the-counter markets, including the OTC Markets-OTCQB tier (the “OTCQB”). In connection with this offering, we intend to apply to have the common stock quoted on the OTCQB or another OTC system. We cannot assure you that the common stock will become eligible for trading on any exchange or market. Until such time as the common stock is quoted on the OTCQB or another public trading market otherwise develops, the selling stockholders identified herein may only sell their shares of common stock pursuant to this prospectus at a fixed price of $3.00 per share, the price per share in the Private Placement discussed above, for a total offering amount of $152,622,267. At and after such time, the selling stockholders may sell all or a portion of their shares through public or private transactions at prevailing market prices or at privately negotiated prices. For more information about how the selling stockholders identified herein may sell shares of our common stock, see the section titled “Shares Eligible for Future Resale” herein.

We may amend or supplement this prospectus from time to time by filing amendments or supplements as required. You should read the entire prospectus and any amendments or supplements carefully before you make your investment decision.

We are an “emerging growth company” and a “smaller reporting company” as defined under the federal securities laws and, as such, are eligible for reduced public company reporting requirements. See “Prospectus Summary — Implications of Being an Emerging Growth Company and a Smaller Reporting Company.”

Investing in our common stock involves a high degree of risk. Before making an investment decision, please read “Risk Factors” beginning on page 6 of this prospectus, and under similar headings in any amendments or supplements to this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2025

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