CXAC C5 Acquisition Corporation

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

OF C5 ACQUISITION CORPORATION

TO BE HELD ON APRIL 6, 2023

To the Stockholders of C5 Acquisition Corporation:

NOTICE IS HEREBY GIVEN that a special meeting of stockholders (the “Special Meeting”) of C5 Acquisition Corporation, a Delaware corporation (“C5,” “we,” “our” or “us”), will be held on April 6, 2023, at 10:00 a.m., Eastern time, via live webcast at the following address: https://www.cstproxy.com/c5acquisitions/2023. You will need the 16-digit meeting control number that is printed on your proxy card to enter the Special Meeting. C5 recommends that you log in at least 15 minutes before the Special Meeting to ensure you are logged in when the Special Meeting starts. Please note that you will not be able to attend the Special Meeting in person. You are cordially invited to attend the Special Meeting for the following purposes:

The purpose of the Extension Amendment Proposal and, if necessary, the Adjournment Proposal, is to allow C5 additional time to complete its initial business combination (a “Business Combination”).

We (using funds held outside the Trust Account) or C5 Sponsor LLC will make monthly deposits directly to the Trust Account in the amount of $0.04, for each outstanding share of Class A common stock, par value $0.0001 per share, up to a maximum of $320,000 per month (each deposit, a “Contribution”) following the approval and implementation of the Extension Amendment Proposal. Contributions will be paid monthly beginning on April 11, 2023 and thereafter on the eleventh day of each month (or if such eleventh day is not a business day, on the business day immediately preceding such eleventh day) until the earliest to occur of (i) the consummation of the Business Combination, (ii) December 11, 2023 and (iii) if the Business Combination is not consummated, the date of liquidation of the Trust Account, as determined in the sole discretion of the Company’s board of directors. Such contributions from the Sponsor will be made pursuant to a non-interest bearing, unsecured promissory note (the “Promissory Note”) issued by the Company to the Sponsor.

The Certificate of Incorporation provides that C5 currently has until April 11, 2023 to complete its initial business combination (the “Termination Date”). C5’s board of directors (the “Board”) has determined that it is in the best interests of C5 to seek an extension of the Termination Date and ask C5’s stockholders approve the Extension Amendment Proposal to allow for additional time to consummate a Business Combination. C5 will call a separate special meeting of its stockholders to approve a Business Combination (referred to herein as a “Business Combination Special Meeting”). The Board believes that it is in the best interests of C5 stockholders that the Extension be obtained so that C5 will have additional time to consummate a Business Combination.

Without the Extension, C5 would not be able to complete a Business Combination on or before the Termination Date. If that were to occur, C5 would be precluded from completing a Business Combination and would be forced to liquidate even if C5’s stockholders are otherwise in favor of consummating a Business

Combination. If the Extension Amendment Proposal is not approved and a Business Combination is not completed on or before the Termination Date, C5 will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem the public shares (the “Class A Common Stock” or “Public Shares”), at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the trust account maintained by Continental Stock Transfer & Trust Company, acting as trustee (the “Trust Account”), including interest (which interest shall be net of taxes payable, and less up to $100,000 of interest to pay dissolution expenses), divided by the number of then outstanding public shares, which redemption will completely extinguish public stockholders’ rights as stockholders (including the right to receive further liquidating distributions, if any), and (iii) as promptly as reasonably possible following such redemption, subject to the approval of the remaining stockholders and the Board in accordance with applicable law, dissolve and liquidate, subject in each case to the C5’s obligations under the Delaware General Corporation Law (the “DGCL”) to provide for claims of creditors and other requirements of applicable law.

If the Extension is approved and implemented, C5 intends to complete a Business Combination as soon as practicable and in any event on or before the Extended Date.

If C5 does not implement the Extension, it will not redeem any Public Shares submitted for Redemption in connection with the Special Meeting.

As contemplated by the Certificate of Incorporation, the holders of C5’s Public Shares may elect to redeem all or a portion of their Class A Common Stock in exchange for their pro rata portion of the funds held in the Trust Account if the Extension is implemented (the “Redemption”).

On the Record Date (as defined below), the redemption price per share was approximately $10.42, based on the aggregate amount on deposit in the Trust Account of approximately $299.6 million as of the Record Date (including interest not previously released to C5 but net of taxes payable), divided by the total number of then outstanding Public Shares. The closing price of the Class A Common Stock on the New York Stock Exchange on the Record Date was $10.37 per share. Accordingly, if the market price of the Class A Common Stock were to remain the same until the date of the Special Meeting, exercising redemption rights would result in a public stockholder receiving approximately $0.05 more per share than if the stock was sold in the open market. C5 cannot assure stockholders that they will be able to sell their Public 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 its securities when such stockholders wish to sell their shares. C5 believes that such redemption right enables its public stockholders to determine whether or not to sustain their investments for an additional period if C5 does not complete a Business Combination on or before the Termination Date.

TO EXERCISE YOUR REDEMPTION RIGHTS, YOU MUST ELECT TO HAVE C5 REDEEM YOUR SHARES FOR A PRO RATA PORTION OF THE FUNDS HELD IN THE TRUST ACCOUNT AND TENDER YOUR SHARES TO C5’S TRANSFER AGENT (EACH, AN “ELECTION” AND COLLECTIVELY, THE “ELECTION”) PRIOR TO 5:00 P.M. EASTERN TIME ON APRIL 4, 2023 (TWO BUSINESS DAYS PRIOR TO THE VOTE AT THE SPECIAL MEETING) (THE “REDEMPTION DEADLINE”). YOU MAY TENDER YOUR SHARES BY EITHER DELIVERING YOUR SHARE CERTIFICATE TO THE TRANSFER AGENT OR BY DELIVERING YOUR SHARES ELECTRONICALLY USING THE DEPOSITORY TRUST COMPANY’S DWAC (DEPOSIT WITHDRAWAL AT CUSTODIAN) SYSTEM. IF THE EXTENSION IS NOT APPROVED, THEN THESE SHARES WILL NOT BE REDEEMED FOR CASH. IF YOU HOLD THE SHARES IN STREET NAME, YOU WILL NEED TO INSTRUCT THE ACCOUNT EXECUTIVE AT YOUR BANK OR BROKER TO WITHDRAW THE SHARES FROM YOUR ACCOUNT IN ORDER TO EXERCISE YOUR REDEMPTION RIGHTS. IF YOU HOLD PUBLIC SHARES THROUGH UNITS, YOU MUST ELECT TO SEPARATE YOUR UNITS INTO THE UNDERLYING PUBLIC SHARES AND PUBLIC

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WARRANTS PRIOR TO EXERCISING YOUR REDEMPTION RIGHTS WITH RESPECT TO THE PUBLIC SHARES.

Immediately following the Redemption Deadline, a public stockholder that makes an Election may withdraw its Election with respect to all or a portion of its public shares for which it previously submitted an Election (an “Election Reversal”). See “The Extension Amendment Proposal—Redemption Withdrawal Procedures.”

TO MAKE AN ELECTION REVERSAL WITH RESPECT TO YOUR PUBLIC SHARES, YOU MUST SUBMIT A WRITTEN REQUEST TO THE TRANSFER AGENT, AFTER 5:00 P.M. EASTERN TIME ON APRIL 4, 2023, THE DATE THAT IS TWO BUSINESS DAYS PRIOR TO THE SCHEDULED VOTE AT THE SPECIAL MEETING, AND PRIOR TO THE SCHEDULED VOTE AT THE SPECIAL MEETING, THAT THE ELECTION TO REDEEM YOUR PUBLIC SHARES BE REVERSED, INCLUDING THE LEGAL NAME, PHONE NUMBER, AND ADDRESS OF THE BENEFICIAL OWNER OF THE SHARES FOR WHICH REVERSAL IS REQUESTED AND THE NUMBER OR PERCENTAGE OF SHARES FOR WHICH REVERSAL IS REQUESTED. IF YOU HOLD THE SHARES IN STREET NAME, YOU WILL NEED TO INSTRUCT THE ACCOUNT EXECUTIVE AT YOUR BANK OR BROKER TO REQUEST REVERSAL OF THE ELECTION TO REDEEM FROM THE TRANSFER AGENT.

Approval of the Extension Amendment Proposal requires the affirmative vote of the holders, as of the Record Date, of at least 65% of all outstanding shares of C5’s Class A Common Stock and Class B Common Stock, par value $0.0001 per share (the “Class B Common Stock” or “founder shares” and, together with the Class A Common Stock, the “Common Stock”), voting together as a single class. C5 will not proceed with the Extension if the number of redemptions of our Public Shares (after taking into account any Election Reversals) causes C5 to have less than $5,000,001 of net tangible assets following approval of the Extension Amendment Proposal.

Record holders of Common Stock at the close of business on March 10, 2023 (the “Record Date”) are entitled to vote or have their votes cast at the Special Meeting. On the Record Date, there were 35,937,500 issued and outstanding shares of Common Stock. C5’s warrants do not have voting rights.

This proxy statement contains important information about the Special Meeting, the Extension Amendment Proposal and the Adjournment Proposal. Whether or not you plan to attend the Special Meeting, C5 urges you to read this material carefully and vote your shares.

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This proxy statement is dated March 16, 2023 and is first being mailed to stockholders on or about that date.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE

SPECIAL MEETING TO BE HELD ON APRIL 6, 2023

This Notice of Special Meeting and Proxy Statement are available at https://www.cstproxy.com/c5acquisitions/2023.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

Certain statements in this proxy statement may constitute “forward-looking statements” for purposes of the federal securities laws. Our forward-looking statements include, but are not limited to, statements regarding our and our management team’s expectations, hopes, beliefs, intentions or strategies regarding the future. In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “goal,” “intends,” “may,” “might,” “outlook,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “target,” “will,” “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Forward-looking statements in this proxy statement may include, for example, statements about:

While forward-looking statements reflect C5’s good faith beliefs, they are not guarantees of future performance. C5 disclaims any obligation to publicly update or revise any forward-looking statement to reflect changes in underlying assumptions or factors, new information, data or methods, future events or other changes after the date of this proxy statement, except as required by applicable law. For a further discussion of these and other factors that could cause C5’s future results, performance or transactions to differ significantly from those expressed in any forward-looking statement, please see the section entitled “Risk Factors” in C5’s Annual Report on Form 10-K for the year ended December 31, 2021, as filed with the Securities and Exchange Commission (the “SEC”) on March 31, 2022, as amended, in C5’s subsequent Quarterly Reports on Form 10-Q and in other reports C5 files with the SEC. You should not place undue reliance on any forward-looking statements, which are based only on information currently available to C5 (or to third parties making the forward-looking statements).

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RISK FACTORS

You should consider carefully all of the risks described in our Annual Report on Form 10-K filed with the SEC on March 29, 2022 and our Quarterly Report on Form 10-Q filed with the SEC on November 14, 2022, and in the other reports we file with the SEC before making a decision on how to vote on the proposals at the Special Meeting. Furthermore, if any of the following events occur, our business, financial condition and operating results may be materially adversely affected, or we could face liquidation. In that event, the trading price of our securities could decline, and you could lose all or part of your investment. The risks and uncertainties described in the aforementioned filings and below are not the only ones we face. Additional risks and uncertainties that we are unaware of, or that we currently believe are not material, may also become important factors that adversely affect our business, financial condition and operating results or result in our liquidation.

There are no assurances that the Extension (as defined below) will enable us to complete a business combination.

Approving the Extension involves a number of risks. Even if the Extension is approved, the Company can provide no assurances that an initial business combination will be consummated prior to the Extended Date (as defined below). Our ability to consummate any business combination is dependent on a variety of factors, many of which are beyond our control. If the Extension is approved, the Company expects to continue to seek a Business Combination (as defined below). The Company then expects to seek stockholder approval of such Business Combination by means of a proxy statement or a proxy statement/prospectus that will be filed with the SEC following the SEC declaring effective a Registration Statement on Form S-4 (a “Business Combination Registration Statement”), to be filed by C5, which will include our preliminary proxy statement/prospectus for such Business Combination.

We are required to offer stockholders the opportunity to redeem shares in connection with the Extension Amendment, and we will be required to offer stockholders redemption rights again in connection with any stockholder vote to approve a Business Combination. Even if the Extension or a Business Combination are approved by our stockholders, it is possible that redemptions will leave us with insufficient cash to consummate a Business Combination on commercially acceptable terms, or at all.

The fact that we will have separate redemption periods in connection with the Extension and a Business Combination vote could exacerbate these risks. Other than in connection with a redemption offer or liquidation, our stockholders may be unable to recover their investment except through sales of our shares on the open market. The price of our shares may be volatile, and there can be no assurance that stockholders will be able to dispose of our shares at favorable prices, or at all.

Regulatory delays could cause us to be unable to consummate a Business Combination.

We are not aware of any material regulatory approvals or actions that are required for completion of a Business Combination besides the SEC’s review of a proxy statement or Business Combination Registration Statement and the expiration or early termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. It is presently contemplated that if any such additional regulatory approvals or actions are required, those approvals or actions will be sought. There can be no assurance, however, that any additional approvals or actions will be obtained. This includes any potential review by a U.S. government entity, such as the Committee on Foreign Investment in the United States (“CFIUS”), on account of certain foreign ownership restrictions on U.S. businesses. We do not believe that either we or our Sponsor constitute, are controlled by or have substantial ties with, a “foreign person” under CFIUS rules and regulations.

Because we have only a limited time to complete our initial business combination, even if we are able to effect the Extension, our failure to obtain any required regulatory approvals in connection with a Business Combination or to resolve the above-mentioned investigations within the requisite time period may require us to

liquidate. If we liquidate, our public stockholders may only receive an amount per share based on the funds available in our Trust Account, and our warrants will expire worthless. This will also cause you to lose any potential investment opportunity in a target company and the chance of realizing future gains on your investment through any price appreciation in the combined company.

We may be subject to a new 1% U.S. federal excise tax in connection with redemptions of our Class A Common Stock.

On August 16, 2022, the Inflation Reduction Act of 2022 (the “IR Act”) was signed into law. The IR Act provides for, among other things, a new 1% U.S. federal excise tax on certain repurchases (including redemptions) of stock by publicly traded U.S. corporations after December 31, 2022. The excise tax is imposed on the repurchasing corporation itself, not its stockholders from whom the shares are repurchased (although it may reduce the amount of cash distributable in a current or subsequent redemption). The amount of the excise tax is generally 1% of any positive difference between the fair market value of any shares repurchased by the repurchasing corporation during a taxable year and the fair market value of certain new stock issuances by the repurchasing corporation during the same taxable year. In addition, a number of exceptions apply to this excise tax. The U.S. Department of the Treasury (the “Treasury”) has been given authority to provide regulations and other guidance to carry out, and prevent the abuse or avoidance of, this excise tax.

On December 27, 2022, the Treasury published Notice 2023-2, which provided clarification on some aspects of the application of the excise tax. The notice generally provides that if a publicly traded U.S. corporation completely liquidates and dissolves, distributions in such complete liquidation and other distributions by such corporation in the same taxable year in which the final distribution in complete liquidation and dissolution is made are not subject to the excise tax. Although such notice clarifies certain aspects of the excise tax, the interpretation and operation of aspects of the excise tax (including its application and operation with respect to SPACs) remain unclear and such interim operating rules are subject to change.

Because the application of this excise tax is not entirely clear, any redemption or other repurchase effected by us, in connection with a business combination, extension vote or otherwise, may be subject to this excise tax. Because any such excise tax would be payable by us and not by the redeeming holder, it could cause a reduction in the value of our Class A Common Stock or cash available for distribution in a subsequent liquidation. Whether and to what extent we would be subject to the excise tax in connection with a business combination will depend on a number of factors, including (i) the structure of the business combination, (ii) the fair market value of the redemptions and repurchases in connection with the business combination, (iii) the nature and amount of any “PIPE” or other equity issuances in connection with the business combination (or any other equity issuances within the same taxable year of the business combination) and (iv) the content of any subsequent regulations, clarifications, and other guidance issued by the Treasury.

The Company has agreed that, to mitigate the current uncertainty surrounding the implementation of the IR Act, funds held in the Trust Account, including any interest thereon, will not be used to pay for any excise tax liabilities with respect to any future redemptions prior to or in connection with the Extension, the Business Combination or the liquidation of the Company.

Changes in laws or regulations, or a failure to comply with any laws and regulations, may adversely affect our business, including our ability to negotiate and complete our initial business combination, and results of operations.

We are subject to laws and regulations enacted by national, regional and local governments. In particular, we are required to comply with certain SEC and other legal requirements. Compliance with, and monitoring of, applicable laws and regulations may be difficult, time consuming and costly. Those laws and regulations and their interpretation and application may also change from time to time and those changes could have a material adverse effect on our business, investments and results of operations. In addition, a failure to comply with

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applicable laws or regulations, as interpreted and applied, could have a material adverse effect on our business, including our ability to negotiate and complete a Business Combination, and results of operations.

On March 30, 2022, the SEC issued proposed rules (the “2022 Proposed Rules”) relating to, among other items, enhancing disclosures in business combination transactions involving SPACs and private operating companies; amending the financial statement requirements applicable to transactions involving shell companies; effectively limiting the use of projections in SEC filings in connection with proposed business combination transactions; increasing the potential liability of certain participants in proposed business combination transactions; and the extent to which SPACs could become subject to regulation under the Investment Company Act. The 2022 Proposed Rules, if adopted, whether in the form proposed or in revised form, and certain positions and legal conclusions expressed by the SEC in connection with the 2022 Proposed Rules, may materially adversely affect our ability to negotiate and complete our Business Combination and may increase the costs and time related thereto.

See also “—We may be subject to a new 1% U.S. federal excise tax in connection with redemptions of our Class A Common stock” and “—If we are deemed to be an investment company under the Investment Company Act, we may be required to institute burdensome compliance requirements and our activities may be restricted, which may make it difficult for us to complete our Business Combination.”

If we are deemed to be an investment company under the Investment Company Act, we may be required to institute burdensome compliance requirements and our activities may be restricted, which may make it difficult for us to complete a Business Combination.

If we are deemed to be an investment company under the Investment Company Act, our activities may be restricted, including, without limitation, restrictions on the nature of our investments, restrictions on the issuance of securities, and restrictions on the enforceability of agreements entered into by us, each of which may make it difficult for us to complete a Business Combination. In addition, we may have imposed upon us burdensome requirements, including, without limitation, registration as an investment company with the SEC (which may be impractical and would require significant changes in, among other things, our capital structure); adoption of a specific form of corporate structure; and reporting, record keeping, voting, proxy and disclosure requirements and compliance with other rules and regulations that we are currently not subject to.

In order not to be regulated as an investment company under the Investment Company Act, unless we can qualify for an exclusion, we must ensure that we are engaged primarily in a business other than investing, reinvesting or trading in securities and that our activities do not include investing, reinvesting, owning, holding or trading “investment securities” constituting more than 40% of our total assets (exclusive of U.S. government securities and cash items) on an unconsolidated basis. Our business is to identify and complete a business combination and thereafter to operate the post-transaction business or assets for the long term. We do not plan to buy businesses or assets with a view to resale or profit from their resale. We do not plan to buy unrelated businesses or assets or to be a passive investor.

The 2022 Proposed Rules under the Investment Company Act would provide a safe harbor for SPACs from the definition of “investment company” under Section 3(a)(1)(A) of the Investment Company Act, provided that they satisfy certain conditions that limit a SPAC’s duration, asset composition, business purpose and activities. The duration component of the proposed safe harbor rule would require a SPAC to file a Current Report on Form 8-K with the SEC announcing that it has entered into an agreement with the target company (or companies) to engage in an initial business combination no later than 18 months after the effective date of the SPAC’s registration statement for its initial public offering. The SPAC would then be required to complete its initial business combination no later than 24 months after the effective date of its registration statement for its initial public offering. Although the 2022 Proposed Rules, including the proposed safe harbor rule, have not yet been adopted, there is uncertainty in the SEC’s view of the applicability of the Investment Company Act to a SPAC that does not complete its initial business combination within the proposed time frame set forth in the proposed safe harbor rule or otherwise falls outside of the other provisions of the safe harbor.

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If we were deemed to be an investment company for purposes of the Investment Company Act, we might be forced to abandon our efforts to complete an initial business combination and instead be required to liquidate. If we are required to liquidate, our investors would not be able to realize the benefits of owning stock in a successor operating business, including the potential appreciation in the value of our stock and warrants following such a transaction, and our warrants would expire worthless. We do not believe that our principal activities currently subject us to the Investment Company Act. To this end, from the time beginning with the consummation of the Company’s initial public offering, the proceeds held in the Trust Account have been invested only in United States “government securities” within the meaning of Section 2(a)(16) of the Investment Company Act having a maturity of 185 days or less or in money market funds meeting certain conditions under Rule 2a-7 promulgated under the Investment Company Act which invest only in direct U.S. government treasury obligations. Pursuant to the trust agreement, the trustee is not permitted to invest in other securities or assets. By restricting the investment of the proceeds to these instruments and by subsequently holding all funds in the Trust Account in cash (as described in the following paragraph), and by having a business plan targeted at acquiring and growing businesses for the long-term (rather than on buying and selling businesses in the manner of a merchant bank or private equity fund), we do not believe we are an “investment company” within the meaning of the Investment Company Act. The initial public offering was not intended for persons seeking a return on investments in government securities or investment securities. The Trust Account is intended as a holding place for funds pending the earliest to occur of: (i) the completion of our primary business objective, which is a business combination; (ii) the redemption of any Public Shares properly submitted in connection with a stockholder vote to amend the Certificate of Incorporation to modify the substance or timing of our obligation to provide for the redemption of our Public Shares in connection with an initial business combination or to redeem 100% of our Public Shares if we do not complete our initial business combination within the completion window; and (iii) absent a business combination, our return of the funds held in the Trust Account to our public stockholders as part of our redemption of the Public Shares. Because we have invested only in permitted instruments, we believe we are not an investment company. If we were deemed to be subject to the Investment Company Act, compliance with these additional regulatory burdens would require additional expenses for which we have not allotted funds and may hinder our ability to consummate our initial business combination. If we are unable to complete a Business Combination on or before the Extended Date, our public stockholders may receive only their pro rata portion of our Trust Account and our warrants will expire worthless.

Since the Sponsor and our directors and officers will lose their entire investment in us if an initial business combination is not completed, they may have a conflict of interest in the approval of the proposals at the Special Meeting.

There will be no distribution from the Trust Account with respect to the founder shares or private placement warrants or their respective underlying shares, which will expire worthless, in the event of our winding up. In the event of a liquidation, our Sponsor and our officers and directors will not receive any monies held in the Trust Account as a result of their ownership of 7,187,500 founder shares that were issued to the Sponsor prior to our initial public offering, which was consummated on January 11, 2022 (“initial public offering” or “IPO”) and 15,035,500 private placement warrants that were purchased by the Sponsor in a private placement which occurred simultaneously with the completion of our IPO. Such persons have waived their rights to liquidating distributions from the Trust Account with respect to these securities, and all of such investments would expire worthless if an initial business combination is not consummated.

Additionally, such persons can earn a positive rate of return on their overall investment in the combined company after an initial business combination, even if other holders of our shares experience a negative rate of return, due to the Sponsor having initially purchased the founder shares for an aggregate of $25,000.

Our Sponsor may extend to us a loan (the “Sponsor Working Capital Loan”) which would be evidenced by promissory notes, which is to be repaid, without interest, upon the date of the consummation of a Business Combination. At the Sponsor’s discretion, up to $2,000,000 of the notes may be converted upon completion of a Business Combination into warrants at a price of $1.00 per warrant. In the event that a Business Combination

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does not close, the Company may use a portion of proceeds held outside the Trust Account to repay the Sponsor Working Capital Loan but no proceeds held in the Trust Account would be used to repay the Sponsor Working Capital Loan. As of September 30, 2022, there were no amounts outstanding under the Sponsor Working Capital Loan.

The completion of a Business Combination will be subject to a number of important conditions, and a Business Combination may be terminated before the completion of such Business Combination in accordance with its terms. As a result, there is no assurance that a Business Combination will be completed.

The completion of a Business Combination will be subject to the satisfaction or waiver, as applicable, of a number of important conditions that will be set forth in the definitive agreement for such Business Combination, including the approval of a Business Combination by the C5 stockholders, the approval of the listing of the combined entity’s shares on New York Stock Exchange (the “NYSE”), and several other customary closing conditions. If these conditions are not satisfied or, if a Business Combination is otherwise terminated by either party, we are unlikely to find another target for a business combination before the Extended Date.

We have incurred and expect to continue to incur significant costs associated with a Business Combination. Whether or not a Business Combination is completed, the incurrence of these costs will reduce the amount of cash available to be used for other corporate purposes by us if a Business Combination is not completed.

We expect to incur significant transaction and transition costs associated with a Business Combination and operating as a public company following the closing of a Business Combination. We may also incur additional costs to retain key employees. Certain transaction expenses incurred in connection with a Business Combination, including all legal, accounting, consulting, investment banking and other fees, expenses and costs, will be paid by the combined company at or following the closing of a Business Combination. Even if a Business Combination is not completed, we expect to incur approximately $800,000 in expenses in aggregate. These expenses will reduce the amount of cash available to be used for other corporate purposes by us if a Business Combination is not completed.

The NYSE may delist our securities from trading on its exchange, which could limit investors’ ability to make transactions in our securities and subject us to additional trading restrictions.

Our Units (as defined below), Class A Common Stock and warrants are listed on the NYSE. We cannot assure you that our securities will continue to be listed on the NYSE in the future, following the Extension or prior to a business combination. In order to continue listing our securities on the NYSE prior to a Business Combination, we must maintain certain financial, distribution and stock price levels. In general, we must maintain a minimum number of holders of our securities. Additionally, in connection with a Business Combination, we will be required to demonstrate compliance with the NYSE’s initial listing requirements, which are more rigorous than the NYSE’s continued listing requirements, in order to continue to maintain the listing of our securities on the NYSE. For instance, our stock price would generally be required to be at least $4 per share. We cannot assure you that we will be able to meet those initial listing requirements at that time.

If the NYSE delists any of our securities from trading on its exchange and we are not able to list such securities on another national securities exchange, we expect such securities could be quoted on an over-the-counter market. If this were to occur, we could face significant material adverse consequences, including:

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The National Securities Markets Improvement Act of 1996, which is a federal statute, prevents or preempts the states from regulating the sale of certain securities, which are referred to as “covered securities.” Because our Units, Class A Common Stock and warrants are listed on the NYSE, our Units, Class A Common Stock and warrants qualify as covered securities under such statute. Although the states are preempted from regulating the sale of our securities, the federal statute does allow the states to investigate companies if there is a suspicion of fraud, and, if there is a finding of fraudulent activity, then the states can regulate or bar the sale of covered securities in a particular case. While we are not aware of a state having used these powers to prohibit or restrict the sale of securities issued by blank check companies, other than the State of Idaho, certain state securities regulators view blank check companies unfavorably and might use these powers, or threaten to use these powers, to hinder the sale of securities of blank check companies in their states. Further, if we were no longer listed on the NYSE, our securities would not qualify as covered securities under such statute and we would be subject to regulation in each state in which we offer our securities.

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QUESTIONS AND ANSWERS ABOUT THE SPECIAL MEETING

The questions and answers below highlight only selected information from this proxy statement and only briefly address some commonly asked questions about the Special Meeting and the proposals to be presented at the Special Meeting. The following questions and answers do not include all the information that is important to C5 stockholders. Stockholders are urged to read carefully this entire proxy statement, including Annex A and the other documents referred to herein, to fully understand the proposals to be presented at the Special Meeting and the voting procedures for the Special Meeting.

C5 is a blank check company incorporated as a Delaware corporation for the purpose of effecting a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or other similar business combination with one or more businesses. On January 11, 2022, C5 consummated its initial public offering of 28,750,000 units (the “Units”), each consisting of one share of Class A Common Stock and one-half of one warrant (the “Public Warrants”). The Units were sold at an offering price of $10.00 per Unit, generating gross proceeds of $287,500,000. Like most blank check companies, C5’s Certificate of Incorporation provides for the return of the initial public offering proceeds held in trust to the holders of the outstanding shares of Class A common stock, par value $0.0001 per share (the “Class A Common Stock” or “Public Shares”), sold in the initial public offering if there is no qualifying business combination(s) consummated on or before the Termination Date.

C5 believes that it is in the best interests of C5’s stockholders to continue C5’s existence until the Extended Date, if necessary, in order to allow C5 additional time to complete a Business Combination and is therefore holding this Special Meeting.

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C5’s board of directors (the “Board”) believes that it is in the best interests of C5 stockholders that the Extension be obtained so that C5 will have additional time to consummate a Business Combination. Without the Extension, C5 would not be able to complete a Business Combination on or before the Termination Date. If that were to occur, C5 would be precluded from completing a Business Combination and would be forced to liquidate even if C5’s stockholders are otherwise in favor of consummating a Business Combination. If the Extension Amendment Proposal is not approved and a Business Combination is not completed on or before the Termination Date, C5 will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem the public shares (the “Class A Common Stock” or “Public Shares”), at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the trust account maintained by Continental Stock Transfer & Trust Company, acting as trustee (the “Trust Account”), including interest (which interest shall be net of taxes payable, and less up to $100,000 of interest to pay dissolution expenses), divided by the number of then outstanding public shares, which redemption will completely extinguish public stockholders’ rights as stockholders (including the right to receive further liquidating distributions, if any), and (iii) as promptly as reasonably possible following such redemption, subject to the approval of the remaining stockholders and the Board in accordance with applicable law, dissolve and liquidate, subject in each case to the C5’s obligations under the Delaware General Corporation Law (the “DGCL”) to provide for claims of creditors and other requirements of applicable law.

If the Extension is approved and implemented, C5 intends to complete a Business Combination as soon as practicable and in any event on or before the Extended Date.

C5 believes that given C5’s expenditure of time, effort and money on a Business Combination, circumstances warrant ensuring that C5 is in the best position possible to consummate a Business Combination and that it is in the best interests of C5’s stockholders that C5 obtain the Extension. C5 believes a Business Combination will provide significant benefits to its stockholders.

You are not being asked to vote on a Business Combination at the Special Meeting. The vote by C5 stockholders on a Business Combination will occur at a separate Business Combination Special Meeting of C5 stockholders and the solicitation of proxies from C5 stockholders in connection with such separate Business Combination Special Meeting, and the related right of C5 stockholders to redeem in connection with such Business Combination (which is a separate right to redeem in addition to the right to redeem in connection with the Extension Amendment Proposal), will be addressed in a Registration Statement on Form S-4 or proxy materials to be filed by C5 at a later date. If you want to ensure your Public Shares are redeemed in the event either the Extension Amendment Proposal is implemented or a Business Combination is completed, you should elect to redeem your Public Shares in connection with either the Special Meeting or the Business Combination Special Meeting, respectively.

Public stockholders may elect (each, an “Election” and collectively, the “Election”) to redeem their Public Shares for a per-share price (the “Per-Share Redemption Price”), payable in cash, equal to the aggregate amount then on deposit in the Trust Account, including interest earned on the funds held in the Trust Account and not previously released to us but net of taxes payable, divided by the number of then outstanding Public Shares, regardless of whether such stockholder votes “FOR” or “AGAINST” the Extension Amendment Proposal.

Immediately following the Redemption Deadline (as defined below), a public stockholder that makes an Election may withdraw its Election with respect to all or a portion of its public shares for which it previously submitted an Election (an “Election Reversal”). See “The Extension Amendment Proposal—Redemption Withdrawal Procedures.”

If the Extension Amendment Proposal is approved and the Extension is completed, we will, pursuant to the investment management trust agreement, remove from the Trust Account an amount (the “Withdrawal Amount”) equal to the number of Public Shares properly redeemed (after taking into account any Election

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Reversals) in connection with the stockholder vote on the Extension Amendment Proposal multiplied by the Per-Share Redemption Price (the “Withdrawal”) and retain the remainder of the funds in the Trust Account for our use in connection with consummating an initial business combination on or before the Extended Date.

If the Extension Amendment Proposal is approved and the Extension is implemented, the removal of the Withdrawal Amount from the Trust Account in connection with the Election (after taking into account any Election Reversals) will reduce the amount held in the Trust Account following the Election. We cannot predict the amount that will remain in the Trust Account following the completion of the Extension and the amount remaining in the Trust Account may be only a small fraction of the approximately $299.6 million that was in the Trust Account as of March 10, 2023. In such event, we may need to obtain additional funds to complete an initial business combination, and there can be no assurance that such funds will be available on terms acceptable to the parties or at all. C5 will not proceed with the Extension if the number of redemptions (after taking into account any Election Reversals) of our Public Shares (after taking into account any Election Reversals) causes C5 to have less than $5,000,001 of net tangible assets following approval of the Extension Amendment Proposal.

Approval of the Adjournment Proposal requires the affirmative vote of a majority of the votes cast by the holders of the shares of Common Stock, voting together as a single class, present in person or represented by proxy at the Special Meeting and entitled to vote thereon. Accordingly, a stockholder’s failure to vote by proxy or to vote in person at the Special Meeting will not be counted towards the number of shares of Common Stock required to validly establish a quorum. However, if a valid quorum is otherwise established, such failure to vote will have no effect on the outcome of any vote on the Adjournment Proposal. Abstentions (but not broker non-votes), while considered present for the purposes of establishing a quorum, will not count as a vote cast at the Special Meeting and will have no effect on the outcome of any vote on the Adjournment Proposal. The presence, in person or by proxy, at the Special Meeting of the holders of shares of outstanding Common Stock representing a majority of the voting power of all issued and outstanding shares of Common Stock entitled to vote as of the Record Date at the Special Meeting shall constitute a quorum for the vote on the Adjournment Proposal.

The Board believes that it is in the best interests of C5 stockholders that the Extension be obtained so that C5 will have additional time to consummate a Business Combination. Without the Extension, C5 would not be able to complete a Business Combination on or before the Termination Date. If that were to occur, C5

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would be precluded from completing a Business Combination and would be forced to liquidate even if C5 stockholders are otherwise in favor of consummating a Business Combination. If the Extension Amendment Proposal is not approved and a Business Combination is not completed on or before the Termination Date, C5 will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten 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 (which interest shall be net of taxes payable, and less up to $100,000 of interest to pay dissolution expenses), divided by the number of then outstanding public shares, which redemption will completely extinguish public stockholders’ rights as stockholders (including the right to receive further liquidating distributions, if any), and (iii) as promptly as reasonably possible following such redemption, subject to the approval of the remaining stockholders and the Board in accordance with applicable law, dissolve and liquidate, subject in each case to the C5’s obligations under the DGCL to provide for claims of creditors and other requirements of applicable law.

If the Extension is approved and implemented, C5 intends to complete a Business Combination as soon as practicable and in any event on or before the Extended Date.

C5 believes that given C5’s expenditure of time, effort and money on a Business Combination, circumstances warrant ensuring that C5 is in the best position possible to consummate a Business Combination and that it is in the best interests of C5’s stockholders that C5 obtain the Extension. C5 believes a Business Combination will provide significant benefits to its stockholders.

If presented, the Board recommends that you vote in favor of the Adjournment Proposal, but expresses no opinion as to whether you should redeem your Public Shares.

The Sponsor and C5’s directors and officers and their respective affiliates are not entitled to redeem any shares of Common Stock in connection with the Extension Amendment Proposal. On the Record Date, the Sponsor and C5’s directors and officers and their respective affiliates beneficially owned and were entitled to vote an aggregate of 7,187,500 shares of Class B Common Stock, representing approximately 20.0% of C5’s issued and outstanding shares of Common Stock.

The Sponsor and the Company’s directors, officers and advisors, or any of their respective affiliates, may purchase Public Shares in privately negotiated transactions or in the open market prior to the Special Meeting, although they are under no obligation to do so. Any such purchases that are completed after the

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Record Date may include an agreement with a selling stockholder that such stockholder, for so long as it remains the record holder of the shares of Common Stock in question, will vote in favor of the proposals and/or will not exercise its redemption rights with respect to the shares of Common Stock so purchased. The purpose of such purchases and other transactions would be to increase the likelihood that the proposals to be voted upon at the Special Meeting are approved by the requisite number of votes. In the event that such purchases do occur, the purchasers may seek to purchase shares from stockholders who would otherwise have voted against the proposals and elected to redeem their shares for a portion of the Trust Account. Any such privately negotiated purchases may be effected at purchase prices that are below or in excess of the per-share pro rata portion of the Trust Account. Any Public Shares held by or subsequently purchased by our affiliates may be voted in favor of the proposals. None of the Sponsor or the Company’s directors, officers or advisors or any of their respective affiliates may make any such purchases when they are in possession of any material nonpublic information not disclosed to the seller or during a restricted period under Regulation M under the Securities Exchange Act of 1934 (the “Exchange Act”).

If you fail to vote by proxy or to vote in person at the Special Meeting, your shares will not be counted in connection with the determination of whether a valid quorum is established and, if a valid quorum is otherwise established, such failure to vote will have the effect of voting “AGAINST” the Extension Amendment Proposal and will have no effect on the outcome of any vote on the Adjournment Proposal.

If you vote to “ABSTAIN” or if you do not provide instructions with your proxy card to your broker, bank or nominee, such abstentions (but not broker non-votes) will be counted in connection with the determination of whether a valid quorum is established, and will have the effect of voting “AGAINST” the Extension Amendment Proposal.

If the Extension Amendment Proposal is approved, the Adjournment Proposal will not be presented for a vote unless C5 determines that additional time is necessary to effectuate the Extension.

If the Extension Amendment Proposal is not approved and a Business Combination is not completed on or before the Termination Date, C5 will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten 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 (which interest shall be net of taxes payable, and less up to $100,000 of interest to pay dissolution expenses), divided by the number of then outstanding public shares, which redemption will completely extinguish public stockholders’ rights as stockholders (including the right to receive further liquidating distributions, if any) and, (iii) as promptly as reasonably possible following such redemption, subject to the approval of the remaining stockholders and the Board in accordance with applicable law, dissolve and liquidate, subject in each case to the C5’s obligations under the DGCL to provide for claims of creditors and other requirements of applicable law.

The Sponsor and the officers and directors of C5 waived their rights to participate in any liquidation distribution from the Trust Account with respect to the 7,187,500 shares of Class B Common Stock held by them. There will be no distribution from the Trust Account with respect to C5’s warrants, which will expire

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worthless in the event C5 dissolves and liquidates the Trust Account. C5 will pay any costs from its remaining assets outside of the Trust Account.

We are seeking approval of the Extension Amendment Proposal because we will not be able to complete all of the tasks listed above prior to April 11, 2023. If the Extension Amendment Proposal is approved, we expect to continue to seek to enter into a definitive agreement for a Business Combination. We then expect to seek stockholder approval of such Business Combination. If stockholders approve a Business Combination, we expect to consummate a Business Combination as soon as practicable following such stockholder approval.

Upon approval of the Extension Amendment Proposal by holders of at least 65% of the Common Stock outstanding as of the Record Date, we will file an amendment to the charter with the Secretary of State of the State of Delaware in the form set forth in Annex A hereto. We will remain a reporting company under the Exchange Act and our Common Stock and Public Warrants are expected to remain publicly traded.

If the Extension Amendment Proposal is approved and the Board decides to implement the Extension Amendment Proposal, we (using funds held outside the Trust Account) or the Sponsor or its designees have agreed to contribute to C5 a loan, referred to herein as the Extension Payment, in the amount equal to $0.04 per share per month, up to a maximum of $320,000 per month, for such extension, to be deposited into the trust account promptly after the Special Meeting. The Extension Payment is conditioned upon the implementation of the Extension Amendment Proposal. No Extension Payment will occur if the Extension Amendment Proposal is not approved. Amounts contributed by the Sponsor in respect of the Extension Payment will not bear interest and will be repayable by the Company to the Sponsor or its designees upon consummation of a Business Combination. If the Company opts not to utilize the Extension Amendment, then the Company will liquidate and dissolve promptly in accordance with the Company’s charter, and the Sponsor’s obligation to make additional contributions will terminate.

Notwithstanding stockholder approval of the Extension Amendment Proposal, our Board will retain the right to abandon and not implement the Extension Amendment at any time without any further action by our stockholders.

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If C5 does not implement the Extension, it will not redeem any Public Shares submitted for Redemption in connection with the Special Meeting.

If you hold shares beneficially in street name and do not provide your broker with voting instructions, your shares may constitute “broker non-votes.” Broker non-votes occur when brokers or others hold shares in street name for a beneficial owner that has not provided instructions on how to vote on a particular matter. Matters on which a broker is not permitted to vote without instructions from the beneficial owner and instructions are not given are referred to as “non-routine” matters. The Adjournment Proposal is considered a routine proposal. Accordingly, your broker, bank or nominee may vote your shares with respect to such proposal without receiving voting instructions. The Extension Amendment Proposal is “non-routine.” In tabulating the voting result for the Proposals, shares that constitute broker non-votes and abstentions are not considered votes cast.

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Your shares will be counted towards the quorum only if you submit a valid proxy (or your broker, bank or other nominee submits one on your behalf) or if you vote in person online at the Special Meeting. Abstentions and broker non-votes will be counted towards the quorum requirement. If there is no quorum, a majority of the shares represented by stockholders present in person online at the Special Meeting or by proxy may authorize adjournment of the Special Meeting to another date.

If on the Record Date your shares were held, not in your name, but rather in an account at a brokerage firm, bank, dealer or other similar organization, then you are the beneficial owner of shares held in “street name” and these proxy materials are being forwarded to you by that organization. As a beneficial owner, you have the right to direct your broker or other agent on how to vote the shares in your account. Alternatively, you may vote by telephone or over the internet as instructed by your broker, banker or other nominee. “Street name” stockholders who wish to vote at the Special Meeting will need the 16-digit meeting control number included on the instructions that accompanied your proxy materials, if applicable, or to obtain a proxy form from your broker, bank or other nominee.

Additionally, the Board has determined that the Adjournment Proposal is in the best interests of C5 and its stockholders and recommends that C5’s stockholders vote “FOR” the Adjournment Proposal.

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With regard to the SEC’s investment company proposals included in the SPAC Rule Proposals, the funds in the Trust Account have been held only in U.S. government treasury bills with a maturity of 185 days or less or in money market funds investing solely in U.S. Treasuries. C5 will continue to invest the funds in the Trust Account in U.S. government treasury bills with a maturity of 185 days or less, in money market funds investing solely in U.S. Treasuries or in interest bearing demand deposit accounts at a bank.

A physical stock certificate will not be needed if your stock is delivered to C5’s transfer agent electronically. In order to obtain a physical stock certificate, a stockholder’s broker and/or clearing broker, DTC. and C5’s transfer agent will need to act to facilitate the request. It is C5’s understanding that stockholders should generally allot at least two weeks to obtain physical certificates from the transfer agent.

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However, because C5 does not have any control over this process or over the brokers or DTC, it may take significantly longer than two weeks to obtain a physical stock certificate. If it takes longer than anticipated to obtain a physical certificate, stockholders who wish to redeem their shares may be unable to obtain physical certificates by the deadline for exercising their redemption rights and thus will be unable to redeem their shares.

Any demand for redemption, once made, may be withdrawn at any time until the deadline for exercising redemption requests, with C5’s consent. If you delivered your shares for redemption to C5’s transfer agent and decide within the required timeframe not to exercise your redemption rights, you may request that C5’s transfer agent return the shares (physically or electronically). You may make such request by contacting C5’s transfer agent at the phone number or address listed under the question “Who can help answer my questions?”

We will not proceed with the Extension if the number of redemptions of our Public Shares (after taking into account any Election Reversals) causes C5 to have less than $5,000,001 of net tangible assets following approval of the Extension Amendment Proposal.

Notwithstanding stockholder approval of the Extension Amendment Proposal or the number of Elections (taking into account any Election Reversals) by our public stockholders, our Board will retain the right to abandon the Extension Amendment Proposal or postpone or cancel the special meeting at any time and for any reason without any further action by our stockholders.

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Mackenzie Partners, Inc.

1407 Broadway – 27th Floor

New York, New York 10018

Call Toll-Free (800) 322-2885

E-mail: proxy@mackenziepartners.com

You may also contact C5 at:

C5 Acquisition Corporation

1701 Pennsylvania Ave NW, Ste #460

Washington, DC 20006

Attention: David Glickman, Chief Financial Officer

E-mail: dglickman@c5acquisitions.com

To obtain timely delivery, C5’s stockholders and warrantholders must request the materials no later than five business days prior to the Special Meeting.

You may also obtain additional information about C5 from documents filed with the SEC by following the instructions in the section entitled “Where You Can Find More Information.”

If you intend to seek redemption of your Public Shares, you will need to send a letter demanding redemption and deliver your stock (either physically or electronically) to C5’s transfer agent prior to 5:00 p.m., New York time, on the second business day prior to the Special Meeting. If you have questions regarding the certification of your position or delivery of your stock, please contact:

Continental Stock Transfer & Trust Company

1 State Street, 30^th Floor

New York, New York 10004

Attention: Mark Zimkind

Email: mzimkind@continentalstock.com

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BACKGROUND

General

C5 is a blank check company formed as a Delaware corporation for the purpose of effecting a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or similar business combination with one or more businesses.

On January 11, 2022, C5 consummated its initial public offering of 28,750,000 Units, which included the full exercise of the underwriters’ over-allotment option. Each Unit consists of one share of Class A Common Stock and one-half of one Public Warrant, with each whole Public Warrant entitling the holder thereof to purchase one share of Class A Common Stock for $11.50 per share. The Units were sold at a price of $10.00 per Unit, generating gross proceeds to the Company of $287,500,000. Simultaneously with the closing of the initial public offering, C5 completed the private placement of an aggregate of 15,035,500 warrants (the “private placement warrants”) to the Sponsor at a purchase price of $1.00 per private placement warrant, generating gross proceeds to the Company of $15,035,500.

Upon the closing of the initial public offering and private placement, $293,250,000 ($10.20 per Unit) of the net proceeds of the sale of the Units  in the initial public offering and the private placement was placed in the Trust Account.

The Proposed Business Combination

The Board currently believes that there will not be sufficient time before April 11, 2023 to complete a Business Combination. Accordingly, the Board believes that in order to be able to consummate a Business Combination, we will need to obtain the Extension. Without the Extension, we believe that we will not be able to complete a Business Combination on or before April 11, 2023. If that were to occur, we would be precluded from completing a Business Combination and would be forced to liquidate even if our stockholders are otherwise in favor of consummating a Business Combination.

The Company’s IPO prospectus and Certificate of Incorporation provide that the affirmative vote of the holders of at least 65% of all outstanding shares of Common Stock is required to extend our corporate existence, except in connection with, and effective upon, consummation of a business combination. Additionally, our IPO prospectus and Certificate of Incorporation provide for all public stockholders to have an opportunity to redeem their Public Shares in the case our corporate existence is extended as described above. Because we continue to believe that a Business Combination would be in the best interests of our stockholders, and because we will not be able to conclude a Business Combination within the permitted time period, the Board has determined to seek stockholder approval to extend the date by which we have to complete a business combination beyond April 11, 2023 to the Extended Date. We intend to hold a Business Combination Special Meeting prior to the Extended Date in order to seek stockholder approval of a Business Combination.

We believe that the foregoing provision in the Certificate of Incorporation was included to protect C5 stockholders from having to sustain their investments for an unreasonably long period if C5 failed to find a suitable business combination in the timeframe contemplated by the Certificate of Incorporation. We also believe that, given the Company’s expenditure of time, effort and money on finding a business combination, circumstances warrant providing public stockholders an opportunity to consider a Business Combination.

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SPECIAL MEETING OF C5 STOCKHOLDERS

The C5 Special Meeting

We are furnishing this proxy statement to our stockholders as part of the solicitation of proxies by our Board for use at the Special Meeting. This proxy statement provides you with information you need to know to be able to vote or instruct your vote to be cast at the Special Meeting.

Date, Time and Place of Special Meeting

The Special Meeting will be held on April 6, 2023, at 10:00 a.m., Eastern Time, conducted via live webcast at the following address https://www.cstproxy.com/c5acquisitions/2023. You will need the control number that is printed on your proxy card to enter the Special Meeting. C5 recommends that you log in at least 15 minutes before the Special Meeting to ensure you are logged in when the Special Meeting starts. Please note that you will not be able to attend the Special Meeting in person.

Proposals at the Special Meeting

At the Special Meeting, C5 will ask the C5 stockholders to vote in favor of the following proposals:

Voting Power; Record Date

You will be entitled to vote or direct votes to be cast at the Special Meeting if you owned shares of Class A Common Stock or Class B Common Stock at the close of business on March 10, 2023, which is the Record Date for the Special Meeting. You are entitled to one vote for each share of Class A Common Stock or Class B Common Stock that you owned as of the close of business on the Record Date. If your shares are held in “street name” or are in a margin or similar account, you should contact your broker, bank or other nominee to ensure that votes related to the shares you beneficially own are properly counted. On the Record Date, there were 28,750,000 shares of Class A Common Stock outstanding and 7,187,500 shares of Class B Common Stock outstanding. All of the outstanding shares of Class B Common Stock are held by our Sponsor.

Our Sponsor has agreed to vote all of their shares of Common Stock in favor of the Extension Amendment Proposal and the Adjournment Proposal. C5’s issued and outstanding warrants do not have voting rights at the Special Meeting.

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Recommendation of the Board

THE BOARD UNANIMOUSLY RECOMMENDS

THAT YOU VOTE “FOR” EACH OF THESE PROPOSALS

Quorum and Required Vote for Proposals for the Special Meeting

The approval of the Extension Amendment Proposal requires the affirmative vote of the holders of at least 65% of all the outstanding shares of Common Stock as of the Record Date. The presence, in person or by proxy, at the Special Meeting of the holders of shares of outstanding Common Stock representing a majority of the voting power of all issued and outstanding shares of Common Stock entitled to vote as of the Record Date at the Special Meeting shall constitute a quorum for the vote on the Extension Amendment Proposal. Accordingly, a C5 stockholder’s failure to vote by proxy or to vote in person at the Special Meeting will not be counted towards the number of shares of Common Stock required to validly establish a quorum, and if a valid quorum is otherwise established, such failure to vote will have the effect of voting “AGAINST” the Extension Amendment Proposal. Abstentions (but not broker non-votes) will be counted in connection with the determination of whether a valid quorum is established, and will have the effect of voting “AGAINST” the Extension Amendment Proposal.

Approval of the Adjournment Proposal requires the affirmative vote of a majority of the votes cast by the holders of the shares of Common Stock, voting together as a single class, present in person or represented by proxy at the Special Meeting and entitled to vote thereon. The presence, in person or by proxy, at the Special Meeting of the holders of shares of outstanding Common Stock representing a majority of the voting power of all issued and outstanding shares of Common Stock entitled to vote as of the Record Date at the Special Meeting shall constitute a quorum for the vote on the Adjournment Proposal. Accordingly, a C5 stockholder’s failure to vote by proxy or to vote in person at the Special Meeting will not be counted towards the number of shares of Common Stock required to validly establish a quorum, but if a valid quorum is otherwise established, such failure to vote will have no effect on the outcome of any vote on the Adjournment Proposal. Abstentions (but not broker non-votes), while considered present for the purposes of establishing a quorum, will not count as a vote cast at the Special Meeting and will have no effect on the outcome of any vote on the Adjournment Proposal.

It is possible that C5 will not be able to complete its initial business combination on or before the Extended Date if the Extension Amendment Proposal is approved. If C5 fails to complete its initial business combination on or before the Extended Date if the Extension Amendment Proposal is approved, C5 will be required to dissolve and liquidate the Trust Account by returning the then remaining funds in such account to the public stockholders.

No Additional Matters

The Special Meeting has been called only to consider and vote on the approval of the Extension Amendment Proposal and the Adjournment Proposal. Under the Company’s bylaws, other than procedural matters incident to the conduct of the Special Meeting, no other matters may be considered at the Special Meeting if they are not included in this proxy statement, which serves as the notice of the Special Meeting.

If C5 does not implement the Extension, it will not redeem any Public Shares submitted for Redemption in connection with the Special Meeting.

Our Board may elect to abandon the Extension Amendment Proposal at any time and for any reason without any further action by our stockholders.

Who Can Answer Your Questions about Voting

If you have any questions about how to vote or direct a vote in respect of your shares of Common Stock, you may call Mackenzie Partners, our proxy solicitor, at (800) 322-2885.

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Redemption Rights

If the Extension Amendment Proposal is approved, and contingent upon the effectiveness of the implementation of the Extension, the Company will provide public stockholders making the Election the opportunity to receive, at the time the Extension becomes effective, and in exchange for the surrender of their Public Shares, a pro rata portion of the funds available in the Trust Account including any interest earned on the funds held in the Trust Account but after permitted withdrawals and net of taxes payable. You will be able to redeem your Public Shares in connection with any stockholder vote to approve a proposed initial business combination or if the Company has not consummated an initial business combination by the Extended Date.

You will be entitled to receive cash for any Public Shares to be redeemed in connection with the Extension Amendment Proposal only if you:

Holders of Public Shares do not need to affirmatively vote on the Extension Amendment Proposal or be a holder of such Public Shares as of the Record Date to exercise redemption rights. If the Extension Amendment Proposal is not approved, these Public Shares will not be redeemed for cash. If a holder of Public Shares properly demands redemption, delivers his, her or its stock certificates (if any) and other redemption forms to Continental, and the Extension Amendment Proposal is consummated, we will redeem each Public Shares for the Per-Share Redemption Price. It is anticipated that this would amount to approximately $10.42 per share. If a holder of Public Shares exercises his, her or its redemption rights, then such holder will be exchanging his, her or its Public Shares for cash and will no longer own such Public Shares.

Holders may demand redemption by delivering their stock certificates (if any) and other redemption forms, either physically or electronically using DTC’s DWAC System, to the Company’s transfer agent prior to the vote at the Special Meeting. If you hold the shares in “street name,” you will have to coordinate with your broker to have your shares certificated or delivered electronically. Certificates that have not been tendered (either physically or electronically) in accordance with these procedures will not be redeemed for cash. There is a nominal cost associated with this tendering process and the act of certificating the shares or delivering them through the DWAC system. The transfer agent will typically charge the tendering broker $100 and it would be up to the broker whether or not to pass this cost on to the redeeming stockholder.

The Company’s transfer agent can be contacted at the following address:

Continental Stock Transfer & Trust Company

1 State Street — 30^th Floor

New York, New York 10004

Attn: Mark Zimkind

Email: mzimkind@continentalstock.com

Furthermore, if a holder of a Public Share delivered its shares in connection with an election of its redemption and subsequently decides prior to the applicable date not to elect to exercise such rights, it may simply request that the transfer agent return the shares (physically or electronically).

The closing price of our Public Shares on March 10, 2023, the Record Date, was $10.37 per share. The cash held in the Trust Account on such date was approximately $299.6 million or $10.42 per public share). Prior to exercising redemption rights, stockholders should verify the market price of Public Shares as they may receive higher proceeds from the sale of their Public Shares in the public market than from exercising their redemption rights if the market price per share is higher than the redemption price. The Company cannot assure its stockholders that they will be able to sell their Public 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 its securities when its stockholders wish to sell their shares.

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If you elect to redeem your Public Shares, you will have no right to participate in, or have any interest in, the future growth of C5, if any. You will be entitled to receive cash for your Public Shares only if you properly and timely demand redemption.

If C5 does not consummate an initial business combination on or before the Termination Date, and the Extension Amendment Proposal is not approved, C5 will be required to dissolve and liquidate the Trust Account by returning the then remaining funds in such account to the public stockholders and all of C5’s warrants will expire worthless.

Your right to redeem your Public Shares in connection with the Special Meeting relating to the Extension Amendment Proposal does not affect the right of C5 stockholders to elect to redeem their Public Shares in connection with a Business Combination, which is a separate and additional redemption right available to continuing C5 stockholders.

If a holder of Public Shares exercises his, her or its redemption rights, then he, she or it will be exchanging its Public Shares for cash and will no longer own those shares.

TO EXERCISE YOUR REDEMPTION RIGHTS, YOU MUST ELECT TO HAVE C5 REDEEM YOUR SHARES FOR A PRO RATA PORTION OF THE FUNDS HELD IN THE TRUST ACCOUNT AND TENDER YOUR SHARES TO C5’S TRANSFER AGENT AT LEAST TWO BUSINESS DAYS PRIOR TO THE VOTE AT THE SPECIAL MEETING. YOU MAY TENDER YOUR SHARES BY EITHER DELIVERING YOUR SHARE CERTIFICATE TO THE TRANSFER AGENT OR BY DELIVERING YOUR SHARES ELECTRONICALLY USING THE DEPOSITORY TRUST COMPANY’S DWAC (DEPOSIT WITHDRAWAL AT CUSTODIAN) SYSTEM. IF THE EXTENSION IS NOT APPROVED, THEN THESE SHARES WILL NOT BE REDEEMED FOR CASH. IF YOU HOLD THE SHARES IN STREET NAME, YOU WILL NEED TO INSTRUCT THE ACCOUNT EXECUTIVE AT YOUR BANK OR BROKER TO WITHDRAW THE SHARES FROM YOUR ACCOUNT IN ORDER TO EXERCISE YOUR REDEMPTION RIGHTS. IF YOU HOLD PUBLIC SHARES THROUGH UNITS, YOU MUST ELECT TO SEPARATE YOUR UNITS INTO THE UNDERLYING PUBLIC SHARES AND PUBLIC WARRANTS PRIOR TO EXERCISING YOUR REDEMPTION RIGHTS WITH RESPECT TO THE PUBLIC SHARES.

In connection with tendering your shares for redemption, prior to 5:00 p.m. Eastern Time on April 4, 2023 (two business days before the Special Meeting), you must elect either to physically tender your stock certificates to Continental Stock Transfer & Trust Company at 1 State Street Plaza, 30^th Floor, New York, New York 10004, Attn: Mark Zimkind, mzimkind@continentalstock.com, or to deliver your Public Shares to Continental electronically using DTC’s DWAC system, which election would likely be determined based on the manner in which you hold your shares. The requirement for physical or electronic delivery prior to 5:00 p.m. Eastern Time on April 4, 2023 (two business days before the Special Meeting) ensures that a redeeming holder’s election is irrevocable once the Extension Amendment Proposal is approved. In furtherance of such irrevocable election, stockholders making the election will not be able to tender their shares after the vote at the Special Meeting.

Through the DWAC system, this electronic delivery process can be accomplished by the stockholders, whether or not it is a record holder or its shares are held in “street name,” by contacting Continental Stock Transfer & Trust Company or its broker and requesting delivery of its shares through the DWAC system. Delivering shares physically may take significantly longer. In order to obtain a physical share certificate, a stockholder’s broker and/or clearing broker, DTC, and the Company’s transfer agent will need to act together to facilitate this request. There is a nominal cost associated with the above-referenced tendering process and the act

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of certificating the shares or delivering them through the DWAC system. Continental Stock Transfer & Trust Company will typically charge the tendering broker $100 and the broker would determine whether or not to pass this cost on to the redeeming holder. It is the Company’s understanding that stockholders should generally allot at least two weeks to obtain physical certificates from the transfer agent. The Company does not have any control over this process or over the brokers or DTC, and it may take longer than two weeks to obtain a physical share certificate. Such stockholders will have less time to make their investment decision than those stockholders that deliver their shares through the DWAC system. Stockholders who request physical stock certificates and wish to redeem may be unable to meet the deadline for tendering their shares before exercising their redemption rights and thus will be unable to redeem their shares.

Certificates that have not been tendered in accordance with these procedures prior to 5:00 p.m. Eastern Time on April 4, 2023 (two business days before the Special Meeting) will not be redeemed for cash held in the Trust Account on the redemption date. In the event that a public stockholder tenders its shares and decides prior to the vote at the Special Meeting that it does not want to redeem its shares, the stockholder may withdraw the tender. If you delivered your shares for redemption to our transfer agent and decide prior to the vote at the Special Meeting not to redeem your Public Shares, you may request that our transfer agent return the shares (physically or electronically). You may make such request by contacting our transfer agent at the address listed above. In the event that a public stockholder tenders shares and the Extension Amendment Proposal is not approved, these shares will not be redeemed and the physical certificates representing these shares will be returned to the stockholder promptly following the determination that the Extension Amendment Proposal will not be approved. If you exercise your redemption rights, you will be exchanging your Public Shares for cash and will no longer own the shares. You will be entitled to receive cash for these shares only if you properly demand redemption and tender your stock certificate(s) to the Company’s transfer agent prior to 5:00 p.m. Eastern Time on April 4, 2023 (two business days before the Special Meeting). The Company anticipates that a public stockholder who tenders shares for redemption in connection with the vote to approve the Extension Amendment Proposal would receive payment of the redemption price for such shares soon after the completion of the Extension. The transfer agent will hold the certificates of public stockholders that make the election until such shares are redeemed for cash or returned to such stockholders. If the Extension Amendment Proposal is not approved or is abandoned, these shares will be returned promptly following the Special Meeting as described above.

Redemption Withdrawal Procedures

Our Board may elect to abandon the Extension Amendment Proposal at any time and for any reason without any further action by our stockholders.

Immediately following the Redemption Deadline to make an Election (which is 5:00 P.M. Eastern time on April 4, 2023, the date that is two business days prior to the scheduled vote at the special meeting), a public stockholder that desires to withdraw its Election may effectuate an Election Reversal. In order to effectuate an Election Reversal, including one for which a commitment has previously been made on the Reversal Commitment Form, you must request that transfer agent return the shares (physically or electronically) as soon as possible after the Redemption Deadline. Such written request shall include your legal name, phone number and address of the beneficial owner of the shares for which reversal is requested. If you hold the shares in street name, you will need to instruct the account executive at your bank or broker to request reversal of the tender from the transfer agent.

TO MAKE AN ELECTION REVERSAL WITH RESPECT TO YOUR PUBLIC SHARES, YOU MUST SUBMIT A WRITTEN REQUEST TO THE TRANSFER AGENT, AFTER 5:00 P.M. EASTERN TIME ON APRIL 4, 2023, THE DATE THAT IS TWO BUSINESS DAYS PRIOR TO THE SCHEDULED VOTE AT THE SPECIAL MEETING, AND PRIOR TO THE SCHEDULED VOTE AT THE SPECIAL MEETING, THAT THE TENDER OF YOUR PUBLIC SHARES BE REVERSED, INCLUDING THE LEGAL NAME, PHONE NUMBER, AND ADDRESS OF THE BENEFICIAL OWNER OF THE SHARES FOR WHICH REVERSAL IS REQUESTED AND THE NUMBER OR

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PERCENTAGE OF SHARES FOR WHICH REVERSAL IS REQUESTED. IF YOU HOLD THE SHARES IN STREET NAME, YOU WILL NEED TO INSTRUCT THE ACCOUNT EXECUTIVE AT YOUR BANK OR BROKER TO REQUEST REVERSAL OF THE ELECTION TO REDEEM FROM THE TRANSFER AGENT.

We will not proceed with the Extension if the number of redemptions of our Public Shares (after taking into account any Election Reversals) causes C5 to have less than $5,000,001 of net tangible assets following approval of the Extension Amendment Proposal or we determine that the Extension is no longer practicable or no longer in the best interest of the Company.

Notwithstanding stockholder approval of the Extension Amendment Proposal or the number of Elections (taking into account any Election Reversals) by our public stockholders, our Board will retain the right to abandon the Extension Amendment Proposal or postpone or cancel the special meeting at any time and for any reason without any further action by our stockholders.

Appraisal or Dissenters’ Rights

No appraisal or dissenters’ rights are available to holders of shares of Common Stock or Warrants in connection with the Extension Amendment Proposal.

Solicitation of Proxies

C5 will pay the cost of soliciting proxies for the Special Meeting. C5 has engaged Mackenzie Partners to assist in the solicitation of proxies for the Special Meeting. C5 has agreed to pay Mackenzie Partners a fee of up to $15,000 in connection with the Extension Amendment. C5 will reimburse Mackenzie Partners for reasonable out-of-pocket expenses and will indemnify Mackenzie Partners and its affiliates against certain claims, liabilities, losses, damages and expenses. C5 also will reimburse banks, brokers and other custodians, nominees and fiduciaries representing beneficial owners of shares of Public Shares for their expenses in forwarding soliciting materials to beneficial owners Public Shares and in obtaining voting instructions from those owners. C5’s directors, officers and employees may also solicit proxies by telephone, by facsimile, by mail, on the Internet or in person. They will not be paid any additional amounts for soliciting proxies.

Interests of the Sponsor and C5’s Directors and Officers

When you consider the recommendation of the Board, C5 stockholders should be aware that aside from their interests as stockholders, the Sponsor and certain members of the Board and officers have interests that are different from, or in addition to, those of other stockholders generally. The Board was aware of and considered these interests, among other matters, in recommending to C5 stockholders that they approve the Extension Amendment Proposal. C5 stockholders should take these interests into account in deciding whether to approve the Extension Amendment Proposal:

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Additionally, if the Extension Amendment Proposal is approved and C5 consummates an initial business combination, the officers and directors may have additional interests as described in the proxy statement/prospectus for such transaction.

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