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The RSUs shall vest on September 29, 2027, subject to the Reporting Person's continued service through each vesting date. Conversion of the RSUs into shares of common stock of the Issuer upon vesting is deferred until the earliest of the following events to occur: (i) a change of control of the Issuer, (ii) a separation of service as a director by the Reporting Person, or (iii) death of the Reporting Person."}],"balance_after":11771267,"source":{"system":"sec-edgar","filing":"0001213900-26-108177","document":"ownership.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000121390026108177/ownership.xml","form_type":"4"}},{"id":851592,"issuer":{"id":5748,"kind":"organization","name":"DEEP FISSION, INC."},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Chief Executive Officer"}}],"security":"Employee Stock Option (right to buy)","published_at":"2026-03-10T17:27:56.000Z","date":"2026-03-09","kind":"grant","planned":false,"acquired":true,"shares":2600000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"Date at which first vesting occurs is indicated. 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The units vest over four years, with 25% of the award vesting on the first anniversary of the December 9, 2025 grant date and the remaining 75% vesting in equal monthly installments thereafter, subject to the Reporting Person's continued service through each vesting date. Restricted stock units do not have an expiration date."}],"balance_after":549451,"source":{"system":"sec-edgar","filing":"0001104659-25-120704","document":"tm2531523-5_4seq1.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000110465925120704/tm2531523-5_4seq1.xml","form_type":"4"}},{"id":991612,"issuer":{"id":9903,"kind":"organization","name":"Deep Isolation Nuclear, Inc.","symbol":"DBHL"},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":true,"officer":false,"ten_percent_owner":true,"other":false}}],"security":"Common Stock","published_at":"2025-11-21T11:12:31.000Z","date":"2025-11-19","kind":"grant","planned":false,"acquired":true,"shares":43333,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F1","text":"Represents the grant of restricted stock units (\"RSUs\"). Each RSU represents a contingent right to receive one share of the Issuer's common stock upon settlement. The RSUs shall fully vest in 1 year and are subject to a deferral based on the earlier to occur of a change of control, a separation of service as a director, and death."}],"balance_after":11748053,"source":{"system":"sec-edgar","filing":"0001213900-25-113423","document":"ownership.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000121390025113423/ownership.xml","form_type":"4"}},{"id":1022378,"issuer":{"id":9903,"kind":"organization","name":"Deep Isolation Nuclear, Inc.","symbol":"DBHL"},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":true,"officer":false,"ten_percent_owner":true,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-10-07T18:48:53.000Z","date":"2025-10-01","kind":"grant","planned":false,"acquired":true,"shares":10833,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"The Stock Option is subject to a 4-year vesting schedule, whereby 1/48th of the option shares will vest monthly beginning on October 1, 2025, subject to Reporting Person's continued service through each vesting date."}],"balance_after":10833,"derivative":{"exercise_price":3,"expiration_date":"2035-10-01","underlying":"Common Shares","underlying_shares":10833},"source":{"system":"sec-edgar","filing":"0001213900-25-097155","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000121390025097155/ownership.xml","form_type":"4"}},{"id":1022377,"issuer":{"id":9903,"kind":"organization","name":"Deep Isolation Nuclear, Inc.","symbol":"DBHL"},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":true,"officer":false,"ten_percent_owner":true,"other":false}}],"security":"Common Stock","published_at":"2025-10-07T18:48:53.000Z","date":"2025-10-01","kind":"grant","planned":false,"acquired":true,"shares":32500,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F1","text":"Represents the grant of restricted stock units (\"RSUs\"). Each RSU represents a contingent right to receive one share of the Issuer's common stock upon settlement. The RSUs are subject to a 4-year vesting period, whereby 1/48th of the RSUs will vest monthly beginning October 1, 2025, subject to the Reporting Person's continuous service through each vesting date."}],"balance_after":11737220,"source":{"system":"sec-edgar","filing":"0001213900-25-097155","document":"ownership.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000121390025097155/ownership.xml","form_type":"4"}},{"id":1045022,"issuer":{"id":5748,"kind":"organization","name":"DEEP FISSION, INC."},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":true,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"President and Chief Executive"}}],"security":"Common Stock","published_at":"2025-09-09T17:16:33.000Z","date":"2025-09-05","kind":"grant","planned":false,"acquired":true,"shares":5057855,"ownership":{"direct":false,"nature":"By Muller Family Trust"},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F1","text":"Received in connection with the Issuer's merger (the \"Merger\") with Deep Fission Inc. (\"Legacy Deep Fission\") in accordance with the terms of the Agreement and Plan of Merger and Reorganization dated as of September 5, 2025, by and among the Issuer (f/k/a Surfside Acquisition Inc.), Deep Fission Acquisition Co. and Legacy Deep Fission (the \"Merger Agreement\"), in exchange for shares of Legacy Deep Fission common stock. Pursuant to the terms of the Merger Agreement, at the effective time of the Merger, each issued and outstanding share of Legacy Deep Fission common stock was converted into the right to receive 17.32142 shares of the Issuer's common stock, rounded to the nearest whole share."},{"field":"ownership.nature","element":"natureOfOwnership","label":"F2","text":"Ms. Muller controls the right to vote and dispose of the shares held by the Muller Family Trust (the \"Trust\") and accordingly, may be deemed to beneficially own the shares held by the Trust. Ms. Muller expressly disclaims beneficial ownership of all securities held by the Trust except to the extent of her pecuniary interest therein."}],"balance_after":5057855,"source":{"system":"sec-edgar","filing":"0001415889-25-023993","document":"form4-09092025_090929.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/2081850/000141588925023993/form4-09092025_090929.xml","form_type":"4"}},{"id":1045021,"issuer":{"id":5748,"kind":"organization","name":"DEEP FISSION, INC."},"owners":[{"id":61805,"kind":"person","name":"Muller Elizabeth","position":1,"cik":"0002081850","reported_name":"Muller Elizabeth","relationship":{"director":true,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"President and Chief Executive"}}],"security":"Common Stock","published_at":"2025-09-09T17:16:33.000Z","date":"2025-09-05","kind":"grant","planned":false,"acquired":true,"shares":5196426,"ownership":{"direct":true},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F1","text":"Received in connection with the Issuer's merger (the \"Merger\") with Deep Fission Inc. 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