FISN · Deep Fission, Inc.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on July 20, 2027, provided the holder continues to provide service through the vesting date.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on July 20, 2027, provided the holder continues to provide service through the vesting date.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on July 20, 2027, provided the holder continues to provide service through the vesting date.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on July 20, 2027, provided the holder continues to provide service through the vesting date.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on the one-year anniversary of the grant date, provided the holder continues to provide service through the vesting date. After the units vest, the holder may elect to defer receipt of the shares until the earlier of a qualifying distribution event or the termination of service, as permitted under the Issuer's equity incentive plan.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on the one-year anniversary of the grant date, provided the holder continues to provide service through the vesting date. After the units vest, the holder may elect to defer receipt of the shares until the earlier of a qualifying distribution event or the termination of service, as permitted under the Issuer's equity incentive plan.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on the one-year anniversary of the grant date, provided the holder continues to provide service through the vesting date. After the units vest, the holder may elect to defer receipt of the shares until the earlier of a qualifying distribution event or the termination of service, as permitted under the Issuer's equity incentive plan.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock upon vesting. The units vest on the one-year anniversary of the grant date, provided the holder continues to provide service through the vesting date. After the units vest, the holder may elect to defer receipt of the shares until the earlier of a qualifying distribution event or the termination of service, as permitted under the Issuer's equity incentive plan.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Each RSU vests based on attainment of both a service-based vesting condition and liquidity event vesting condition, in each case, prior to the expiration date. 25% of the service-based vesting condition will be satisfied on the one-year anniversary of the grant date and the remainder in equal monthly installments thereafter, subject to the reporting person's continued service through the vesting dates. The liquidity event condition will be satisfied on the earliest to occur of a change in control, initial public offering or direct listing.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Each restricted stock unit gives the holder the right to receive one share of the Issuer's common stock upon vesting. The units vest after six months, as long as the holder continues to provide service through the vesting date. After the units vest, the holder may choose to delay receiving the shares until the earlier of a qualifying distribution event or the end of service, as allowed under the Issuer's equity incentive plan.

These restricted stock units do not have an expiration date.

The stock options 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.

Each restricted stock unit represents the contingent right to receive one share of the Issuer's common stock upon vesting. 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.

Each restricted stock unit gives the holder the right to receive one share of the Issuer's common stock upon vesting. The units vest after six months, as long as the holder continues to provide service through the vesting date. After the units vest, the holder may choose to delay receiving the shares until the earlier of a qualifying distribution event or the end of service, as allowed under the Issuer's equity incentive plan.

These restricted stock units do not have an expiration date.

Each restricted stock unit gives the holder the right to receive one share of the Issuer's common stock upon vesting. The units vest after six months, as long as the holder continues to provide service through the vesting date. After the units vest, the holder may choose to delay receiving the shares until the earlier of a qualifying distribution event or the end of service, as allowed under the Issuer's equity incentive plan.

These restricted stock units do not have an expiration date.

Each restricted stock unit gives the holder the right to receive one share of the Issuer's common stock upon vesting. The units vest after six months, as long as the holder continues to provide service through the vesting date. After the units vest, the holder may choose to delay receiving the shares until the earlier of a qualifying distribution event or the end of service, as allowed under the Issuer's equity incentive plan.

These restricted stock units do not have an expiration date.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

Date at which first vesting occurs is indicated. One-fourth of the total number of options to purchase the Company's common stock vests on the first vesting date shown and an additional one-thirty sixth on each month thereafter until fully vested.

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.

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.

As a condition under the terms of an Agreement and Plan of Merger and Reorganization, dated as of September 5, 2025, and pursuant to the terms of a stock cancellation agreement, the reporting person voluntarily surrendered and cancelled for no consideration 2,833,333 shares of Issuer's common stock prior to the consummation of the Merger on September 5, 2025. The reporting person resigned as a director of the Issuer upon consummation of the Merger.

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.

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.

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.