SilverBox Corp IV

The extraordinary general meeting (the “Extraordinary General Meeting”) of SilverBox Corp IV (“we,” “us,” “our” or the “Company”) will be held at 10:00 a.m. Eastern Time on August 11, 2026 at the offices of Paul Hastings LLP, located at 515 South Flower Street, Twenty-Fifth Floor, Los Angeles, CA 90071, or at such other time, on such other date and at such other place to which the meeting may be postponed or adjourned, or to attend virtually via the Internet. You will be able to attend the Extraordinary General Meeting online, vote, view the list of shareholders entitled to vote at the Extraordinary General Meeting and submit your questions during the Extraordinary General Meeting by visiting https://www.cstproxy.com/silverboxcorpiv/ext2026 or by phone dialing within the U.S. and Canada 1 800-450-7155 (toll-free) or outside of the U.S. and Canada +1 857-999-9155 (standard rates apply) and entering the conference identification number 1417287#. The sole purpose of the Extraordinary General Meeting is to consider and vote upon the following proposals:

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a proposal to amend the Company’s amended and restated memorandum and articles of association (the “Articles”) pursuant to an amendment to the Articles in the form set forth in Annex A to this Proxy Statement (the “Extension Amendment” and, such proposal, the “Extension Amendment Proposal”) to extend the date by which the Company must (1) consummate a merger, amalgamation, share exchange, asset acquisition, share purchase, reorganization or similar business combination with one or more businesses (a “business combination”), (2) cease its operations except for the purpose of winding up if it fails to complete such business combination, and (3) redeem all of the Company’s Class A ordinary shares included as part of the units sold in the Company’s initial public offering that was consummated on August 19, 2024 (the “IPO”), from August 19, 2026 to December 19, 2026 (the “Extension” and, such date, the “Extended Date”); and

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a proposal to amend the Articles pursuant to an amendment to the Articles in the form set forth in Annex B to the Proxy Statement (the “Redemption Limitation Amendment” and such proposal, the “Redemption Limitation Amendment Proposal”) to eliminate the limitation that the Company may not redeem the Class A ordinary shares included as part of the units sold in the Company’s IPO (collectively, the “public shares” and, individually, each a “public share”) to the extent that such redemption would result in the Company having net tangible assets (as determined in accordance with Rule 3a51-1(g)(1) of the Securities Exchange Act of 1934 (the “Exchange Act”)) to be less than $5,000,001 (the “Redemption Limitation”) in order to allow the Company to redeem public shares irrespective of whether such redemption would exceed the Redemption Limitation; and

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a proposal to approve the adjournment of the Extraordinary General Meeting to a later date or dates, if necessary, (i) to permit further solicitation and vote of proxies in the event that there are insufficient votes for, or otherwise in connection with, the approval of the Extension Amendment Proposal or the Redemption Limitation Amendment Proposal or (ii) where our board of directors has determined it is otherwise necessary (the “Adjournment Proposal”). The Adjournment Proposal will only be presented at the Extraordinary General Meeting if there are not sufficient votes to approve the Extension Amendment Proposal.

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The purpose of the Extension Amendment and the Redemption Limitation Amendment are to allow us more time to complete our previously announced business combination with Parataxis Holdings Inc. (the “Proposed Business Combination”). The Articles provide that we have until August 19, 2026 to complete our initial business combination. As we are continuing to work on the registration statement and proxy

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statement relating to the Proposed Business Combination, our board of directors (our “board”) believes that there will not be sufficient time before August 19, 2026 to hold an extraordinary general meeting at which to conduct a vote for the shareholder approvals required in connection with the Proposed Business Combination and to consummate the Proposed Business Combination. Accordingly, our board believes that in order for our shareholders to evaluate the Proposed Business Combination and for us to be able to consummate the Proposed Business Combination, we will need to obtain the Extension.

Approval of the Extension Amendment Proposal and the Redemption Limitation Amendment Proposal are a condition to the implementation of the Extension.

In connection with the Extension Amendment Proposal and the Redemption Limitation Amendment Proposal, shareholders may elect to redeem their Class A ordinary shares for a per-share price, payable in cash, equal to the aggregate amount then on deposit in the Trust Account, including interest earned, divided by the number of then outstanding Class A ordinary shares included as part of the units sold in the IPO (including any shares of common stock issued in exchange thereof, the “public shares”), and which election we refer to as the “Election.” An Election can be made regardless of whether such public shareholders vote “FOR” or “AGAINST” the Extension Amendment Proposal and the Redemption Limitation Amendment Proposal and an Election can also be made by public shareholders who do not vote, or do not instruct their broker or bank how to vote, at the Extraordinary General Meeting. Holders of public shares (the “public shareholders”) may make an Election regardless of whether such public shareholders were holders as of the record date. Public shareholders who do not make the Election would be entitled to have their shares redeemed for cash if we have not completed our initial business combination by the Extended Date. In addition, regardless of whether public shareholders vote “FOR” or “AGAINST” the Extension Amendment Proposal and the Redemption Limitation Amendment Proposal, or do not vote, or do not instruct their broker or bank how to vote, at the Extraordinary General Meeting, if the Extension is implemented and a public shareholder does not make an Election, they will retain the right to vote on any proposed initial business combination in the future, including the Proposed Business Combination, if applicable, and the right to redeem their public shares at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the Trust Account as of two business days prior to the consummation of such initial business combination, including interest (which interest shall be net of taxes payable), divided by the number of then outstanding public shares, in the event a proposed business combination, including the Proposed Business Combination, if applicable, is completed. We are not asking you to vote on any proposed business combination, including the Proposed Business Combination, at this time. We will seek approval of the Proposed Business Combination, among other things, at a separate extraordinary general meeting pursuant to a separate proxy statement/prospectus. If the Extension Amendment and the Redemption Limitation Amendment are not approved, we may not be able to consummate the Proposed Business Combination before August 19, 2026. We urge you to vote at the Extraordinary General Meeting regarding the Extension Amendment and the Redemption Limitation Amendment. In addition, if you elect to redeem your shares at this time in connection with the Extension, sufficient cash amounts may not remain in the Trust Account to permit the Company to satisfy a related closing condition that is set forth in the business combination agreement relating to the Proposed Business Combination. As a result, while Parataxis would have the right to waive any related closing condition in certain circumstances, the Proposed Business Combination may not be consummated if there is not a sufficient amount of cash in the Trust Account as a result of redemptions of our shares in connection with the Extension, even if our shareholders vote to approve the Extension.

The withdrawal of funds from the Trust Account in connection with the Election will reduce the amount held in the Trust Account following the Election, and the amount remaining in the Trust Account may be only a small fraction of the approximately $217,134,228 that was in the Trust Account as of June 30, 2026. In such event, we may need to obtain additional funds to complete the Proposed Business Combination or any other initial business combination, and there can be no assurance that such funds will be available on terms acceptable or at all.

The Adjournment Proposal, if adopted, will allow our board to adjourn the Extraordinary General Meeting to a later date or dates to permit further solicitation of proxies. The Adjournment Proposal will only be presented to our shareholders (i) in the event that there are insufficient votes for, or otherwise in connection with, the approval of the Extension Amendment Proposal or the Redemption Limitation Amendment Proposal or (ii) where the Board has determined it is otherwise necessary.

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If the Extension Amendment Proposal and the Redemption Limitation Amendment Proposal are not approved and we do not consummate our initial business combination by August 19, 2026, as contemplated by our IPO prospectus and in accordance with our Articles, we will: (1) cease all operations except for the purpose of winding up; (2) as promptly as reasonably possible but not more than 10 business days thereafter, redeem the public shares, at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the Trust Account, including interest (less up to $100,000 of interest to pay dissolution expenses and which interest shall be net of taxes payable), divided by the number of then issued and outstanding public shares, which redemption will completely extinguish public shareholders’ rights as shareholders (including the right to receive further liquidation distributions, if any); and (3) as promptly as reasonably possible following such redemption, subject to the approval of our remaining shareholders and our board, dissolve and liquidate, subject in each case to our obligations under Cayman Islands law to provide for claims of creditors and the requirements of other applicable law.

There will be no redemption rights or liquidating distributions with respect to our warrants, which will expire worthless in the event of our winding up. In the event of a liquidation, the holder of our Class B ordinary shares (the “founder shares” and, together with the public shares, the “shares” or “ordinary shares”), SilverBox Sponsor IV LLC (“Sponsor”) will not receive any monies held in the Trust Account as a result of its ownership of the founder shares.

Based upon the amount in the Trust Account as of June 30, 2026, which was $217,134,228, we anticipate that the per-share price at which public shares will be redeemed from cash held in the Trust Account will be approximately $10.85 at the time of the Extraordinary General Meeting. The closing price of the public shares on the New York Stock Exchange (the “NYSE”) on July 16, 2026, the most recent practicable closing price prior to the mailing of this Proxy Statement, was $10.80. We cannot assure shareholders that they will be able to sell their shares in the open market, even if the market price per share is higher than the redemption price stated above, as there may not be sufficient liquidity in our securities when such shareholders wish to sell their shares.

If the Extension Amendment Proposal is approved, we will (1) remove from the Trust Account an amount (the “Withdrawal Amount”) equal to the number of public shares properly redeemed multiplied by the per-share price, equal to the aggregate amount then on deposit in the Trust Account, including interest earned, divided by the number of then outstanding public shares and (2) deliver to the holders of such redeemed public shares their pro rata portion of the Withdrawal Amount. The remainder of such funds will remain in the Trust Account and will be available for use by us in connection with consummating an initial business combination on or before the Extended Date. Holders of public shares who do not redeem their public shares now will retain their redemption rights and their ability to vote on any initial business combination, including the Proposed Business Combination, if applicable, through the Extended Date if the Extension Amendment Proposal is approved.

Our board has fixed the close of business on July 17, 2026 as the record date for determining our shareholders entitled to receive notice of and vote at the Extraordinary General Meeting and any postponement or adjournment thereof. Only holders of record of the ordinary shares on that date are entitled to have their votes counted at the Extraordinary General Meeting or any postponement or adjournment thereof. On the record date of the Extraordinary General Meeting, there were 25,455,000 ordinary shares outstanding, of which 20,455,000 were public shares and 5,000,000 were founder shares. The founder shares carry voting rights in connection with the Extension Amendment Proposal, the Redemption Limitation Amendment Proposal and the Adjournment Proposal, and we have been informed by our Sponsor and the other initial shareholders, which hold all founder shares, that they intend to vote in favor of the Extension Amendment Proposal, the Redemption Limitation Amendment Proposal and the Adjournment Proposal.

This Proxy Statement contains important information about the Extraordinary General Meeting and the proposals. Please read it carefully and vote your shares.

We will pay for the entire cost of soliciting proxies. We have engaged Sodali & Co. (“Sodali”), to assist in the solicitation of proxies for the Extraordinary General Meeting. We have agreed to pay Sodali a fee of $20,000. We will also reimburse Sodali for reasonable out-of-pocket expenses and will indemnify Sodali and its affiliates against certain claims, liabilities, losses, damages and expenses. In addition to these mailed

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proxy materials, our directors and officers may also solicit proxies in person, by telephone or by other means of communication. These parties will not be paid any additional compensation for soliciting proxies. We may also reimburse brokerage firms, banks and other agents for the cost of forwarding proxy materials to beneficial owners.

This Proxy Statement is dated July 17, 2026 and is first being mailed to shareholders on or about July 17, 2026.

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