SCHEDULE 13G/A: Statement of Beneficial Ownership by Certain Investors
Published on November 13, 2026
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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549 | |
SCHEDULE 13G | |
UNDER THE SECURITIES EXCHANGE ACT OF 1934
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(Amendment No. 3)
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DEEP FISSION, INC. (Name of Issuer) | |
Common Stock, par value $0.0001 per share (Title of Class of Securities) | |
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09/30/2026 (Date of Event Which Requires Filing of this Statement) |
| Check the appropriate box to designate the rule pursuant to which this Schedule is filed: |
 Rule 13d-1(b)
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 Rule 13d-1(c)
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| Rule 13d-1(d)
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SCHEDULE 13G
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| CUSIP Number(s): | 243927100 |
| 1 | Names of Reporting Persons
Tompkins Mark N. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
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| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
CANADA (FEDERAL LEVEL)
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| Number of Shares Beneficially Owned by Each Reporting Person With: |
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| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
2,026,767.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
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| 11 | Percent of class represented by amount in row (9)
3.4 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
IN |
Comment for Type of Reporting Person: With respect to Row (11), the percentage is calculated based on 59,779,233 shares of Common Stock of the Issuer issued and outstanding as of September 30, 2026, as reported by the Issuer in its Quarterly Report on Form 10-Q filed with the SEC on November 4, 2026.
SCHEDULE 13G
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| Item 1. | ||
| (a) | Name of issuer:
DEEP FISSION, INC. | |
| (b) | Address of issuer's principal executive offices:
2001 Addison St., Suite 300 Berkeley, CA 94704 | |
| Item 2. | ||
| (a) | Name of person filing:
Mark N. Tompkins | |
| (b) | Address or principal business office or, if none, residence:
Apt. 1, Via Guidino 23 6900 Lugano-Paradiso, Switzerland | |
| (c) | Citizenship:
Canada | |
| (d) | Title of class of securities:
Common Stock, par value $0.0001 per share | |
| (e) | CUSIP No.:
243927100 | |
| Item 3. | If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a: | |
| (a) | Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
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| (b) | Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
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| (c) | Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
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| (d) | Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
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| (e) | An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
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| (f) | An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
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| (g) | A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
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| (h) | A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
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| (i) | A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
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| (j) | A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution: | |
| (k) | Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
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| Item 4. | Ownership | |
| (a) | Amount beneficially owned:
2,026,767 | |
| (b) | Percent of class:
3.4 %
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| (c) | Number of shares as to which the person has:
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| (i) Sole power to vote or to direct the vote:
2,026,767 | ||
| (ii) Shared power to vote or to direct the vote:
0 | ||
| (iii) Sole power to dispose or to direct the disposition of:
2,026,767 | ||
| (iv) Shared power to dispose or to direct the disposition of:
0 | ||
| Item 5. | Ownership of 5 Percent or Less of a Class. | |
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Ownership of 5 percent or less of a class
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| Item 6. | Ownership of more than 5 Percent on Behalf of Another Person. | |
Not Applicable
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| Item 7. | Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person. | |
Not Applicable
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| Item 8. | Identification and Classification of Members of the Group. | |
Not Applicable
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| Item 9. | Notice of Dissolution of Group. | |
Not Applicable
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| Item 10. | Certifications: |
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. |
| 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.
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