DEEP FISSION, INC.

Insider Trading Arrangements and Policies

During the quarter ended September 30, 2026, certain of the Company’s directors and officers (as defined in Rule 16a-1(f) of the Exchange Act) adopted a “Rule 10b5-1 trading arrangement” with respect to the Company’s common stock, as described below, in order to satisfy tax obligations upon the vesting and settlement of restricted stock units. Each arrangement is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) and permits transactions to commence only after expiration of the applicable cooling-off period required by Rule 10b5-1. Other than the adoptions described below, no other director or officer of the Company adopted or terminated a “Rule 10b5-1 trading arrangement” or “non-Rule 10b5-1 trading arrangement” (in each case, as defined in Item 408 of Regulation S-K).

1 Sales are scheduled to begin on March 2, 2027. Each trading arrangement will terminate on the earliest to occur of: (a) one (1) year after the date the broker begins executing sales under the arrangement, (b) the execution of all trades contemplated under the arrangement; (c) promptly after the broker receives written notice that the director or officer has filed a petition for bankruptcy or insolvency, or that such a petition has been filed against the director or officer and not dismissed within sixty (60) days of its filing, or of the director’s or officer’s liquidation or dissolution; (d) promptly after the broker receives written notice of the director’s or officer’s death or legal incapacity; (e) at any time upon one day’s prior written notice by the director or officer to the broker; (f) upon a reasonable determination by the broker, or promptly after a reasonable determination by the director or officer and notice to the broker, that the arrangement does not comply with Rule 10b5-1 or other applicable securities laws, that the director or officer or the broker has not complied with the arrangement, Rule 10b5-1 or other applicable securities laws, or that the director or officer has made misstatements in the representations or warranties in the arrangement; (g) the broker’s receipt of written notice from the Company or the director or officer of the filing of a bankruptcy petition by the Company, the public announcement of a merger, recapitalization, acquisition, tender or exchange offer or other business combination or reorganization resulting in the exchange or conversion of the Company’s common stock into shares of another company, or the conversion of the Company’s common stock into rights to receive fixed amounts of cash or into debt securities or preferred stock; (h) immediately upon the director’s or officer’s failure to deliver shares as required under the arrangement; (i) the occurrence of another termination event specified in the arrangement; or (j) immediately after written notification from the Company’s Chief Financial Officer that the arrangement is terminated due to a decision by the Company to net settle the tax and other liabilities that are the reason for the arrangement.

Shelf Registration Statement

Concurrently with the filing of this Quarterly Report, the Company intends to file a shelf registration statement on Form S-3 (the “Shelf Registration Statement”) with the SEC. The Company is filing the Shelf Registration Statement for general corporate housekeeping purposes in order to provide the Company with flexibility to access the capital markets from time to time in the future. The Shelf Registration Statement has not yet been declared effective by the SEC, and securities may not be sold, nor may offers to buy be accepted, prior to the time the Shelf Registration Statement becomes effective. This Quarterly Report shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

Non-Affiliate Market Shares and Value

As of October 30, 2026, more than 5% of the Company’s outstanding shares of common stock, its only class of voting securities, were held by stockholders other than its directors, executive officers, holders of 10% or more of its common stock and their respective affiliates, and were not subject to lock-up or other contractual transfer restrictions.