# EDGAR Filing Document

**Accession Number:** 0002081872
**File Stem:** 0001213900-25-090841
**Filing Date:** 2025-9
**Character Count:** 9527
**Document Hash:** 4f055d5a5958237f795ca94e04776c75
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001213900-25-090841.hdr.sgml**: 20250923

**ACCESSION NUMBER**: 0001213900-25-090841

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20250923

**DATE AS OF CHANGE**: 20250923

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** DEEP FISSION, INC.
- **CENTRAL INDEX KEY:** 0001918102
- **STANDARD INDUSTRIAL CLASSIFICATION:** ELECTRIC SERVICES [4911]
- **ORGANIZATION NAME:** 01 Energy & Transportation
- **EIN:** 874265302
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-93944
- **FILM NUMBER:** 251335077

**BUSINESS ADDRESS:**
- **STREET 1:** 55 NE 5TH AVE
- **STREET 2:** SUITE 401
- **CITY:** BOCA RATON
- **STATE:** FL
- **ZIP:** 33432
- **BUSINESS PHONE:** 561 464 2841

**MAIL ADDRESS:**
- **STREET 1:** 55 NE 5TH AVE
- **STREET 2:** SUITE 401
- **CITY:** BOCA RATON
- **STATE:** FL
- **ZIP:** 33432

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Surfside Acquisition Inc.
- **DATE OF NAME CHANGE:** 20220317
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Muller Richard
- **CENTRAL INDEX KEY:** 0002081872

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D

**MAIL ADDRESS:**
- **STREET 1:** 2831 GERBER STREET
- **CITY:** BERKELEY
- **STATE:** CA
- **ZIP:** 94705

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

## SCHEDULE 13D

### Under the Securities Exchange Act of 1934

**DEEP FISSION, INC.**

*(Name of Issuer)*

**Common Stock, $0.0001 par value per share**

*(Title of Class of Securities)*

**243927100**

*(CUSIP Number)*

**Richard Muller**<br>2831 Garber Street<br>Berkeley CA 94705<br>(707) 400-0778

*(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)*

**09/05/2025**

*(Date of Event Which Requires Filing of this Statement)*

| **CUSIP No.** | **243927100** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Muller Richard** | Name of reporting person<br>**Muller Richard** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**OO** | Source of funds (See Instructions)<br>**OO** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**5426406.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**5426406.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5426406.00** | Aggregate amount beneficially owned by each reporting person<br>**5426406.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**10.6%** | Percent of class represented by amount in Row (11)<br>**10.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for Reporting Person:** Comments to items 7, 9, and 11: Consists of (i) 5,196,423 shares of common stock of the Issuer (the "Common Stock") held directly by Richard Muller, (ii) 202,926 shares of Common Stock issuable for vested and exercisable stock options issued pursuant to the Issuer's pre-Merger 2025 Equity Incentive Plan ("2025 Plan"), and (iii) 27,057 shares of Common Stock issuable pursuant to stock options exercisable within 60 days of September 19, 2025.

Comments to item 13: The calculation is based on dividing (i) the aggregate number of shares of Common Stock beneficially owned by the Reporting Person as set forth in Row 11 by (ii) the sum of (a) 50,874,809 shares of Common Stock reported by the Issuer to be outstanding as of September 19, 2025 and (b) 27,057 shares of Common Stock issuable to the Reporting Person pursuant to stock options exercisable within 60 days of September 19, 2025.

**Item 1. Security and Issuer**

**(a) Title of Class of Securities:**
Common Stock, $0.0001 par value per share

**(b) Name of Issuer:**
DEEP FISSION, INC.

**(c) Address of Issuer's Principal Executive Offices:**
2831 Garber Street, Berkeley, CA, 94705

**Item 4. Purpose of Transaction**

The Reporting Person acquired the Common Stock in connection with the Merger. The information contained in Item 3 of this Schedule 13D is incorporated herein by reference.

The Reporting Person serves as a Director and Chief Technology Officer of the Issuer. Accordingly, the Reporting Person may have influence over the corporate activities of the Issuer, including activities that may relate to items described in clauses (a) through (j) of Item 4 of this Schedule 13D. Subject to the Registration Rights Agreement described in Item 6 of this Schedule 13D, the Reporting Person may, from time to time, purchase or sell securities of the Issuer as appropriate for his personal circumstances. Except as described in this Schedule 13D, the Reporting Person does not have any present plans or proposals that relate to or would result in any of the actions described in clauses (a) through (j) of Item 4 of this Schedule 13D. The Reporting Person reserves the right to formulate plans and/or proposals and to take such actions with respect to his investment in the Issuer, including any or all of the actions set forth in clauses (a) through (j) of Item 4 of this Schedule 13D.

**Item 5. Interest in Securities of the Issuer**

**(a)**
The aggregate percentage of Common Stock that the Reporting Person may be deemed to beneficially own is determined in accordance with the rules of the SEC and is based on 50,874,809 shares of Common Stock issued and outstanding as of September 5, 2025, as reported in the Issuer's Current Report on Form 8-K filed with the SEC on September 11, 2025 (the "Super 8-K"). Based on the foregoing, the Reporting Person may be deemed to beneficially own 20% of the Issuer's Common Stock in the aggregate, rounded to the nearest tenth. As of the Closing Date, the Reporting Person beneficially owned, in the aggregate, 5,426,406 shares of Common Stock, comprising (i) 5,196,423 shares of Common Stock, held directly by Richard Muller, (ii) 202,926 shares of Common Stock issuable for vested and exercisable stock options issued pursuant to the Issuer's 2025 Plan, and (iii) 27,057 shares of Common Stock issuable pursuant to stock options exercisable within 60 days of September 19, 2025.

**(b)**
As a result of the Transactions, the Reporting Person is the beneficial owner of, and has the sole power to vote or direct the vote and to dispose or to direct the disposition of 5,426,406 shares of Common Stock, which includes 27,057 shares of Common Stock underlying options which are exercisable within 60 days of September 19, 2025.

**(c)**
Except as set forth in this Schedule 13D, there have been no other reportable transactions with respect to the Common Stock within the last 60 days by the Reporting Person.

**Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.**

Registration Rights Agreement

In connection with the Merger, on September 5, 2025, the Issuer entered into a registration rights agreement (the "Registration Rights Agreement"), pursuant to which, the Issuer has agreed that promptly, but no later than 45 calendar days after the date on which the Super 8-K is first filed by the Issuer with the SEC, the Issuer will file, subject to customary exceptions, a registration statement with the SEC, covering, among other securities, the shares of Common Stock issued to Legacy Deep Fission's stockholders as a result of the Merger and the related share conversion.

Lock-Up Agreement

The Reporting Person has entered into a lock-up agreement pursuant to which it has agreed not to, except in limited circumstances, offer, pledge, sell, contract to sell, transfer or dispose of, directly or indirectly, or engage in swap or similar transactions with respect to, any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock, including, as applicable, shares received in the Merger and issuable upon exercise of certain options, for a period of 180 days after the listing of the Common Stock on a national securities exchange.

### SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** Muller Richard

**Signature:** /s/ Richard Muller

**Name/Title:** Richard Muller/Director

**Date:** 09/23/2025