Hyliion Holdings Corp.

Shares that are properly voted via the Internet, mobile device, or by telephone or for which proxy cards are properly executed and returned will be voted at the Annual Meeting in accordance with the directions given or, in the absence of directions, will be voted in accordance with the Board’s recommendations as follows: “FOR” the election of each of the nominees to the Board named herein, “FOR” the ratification of the appointment of our independent auditors, “FOR” the approval, on an advisory basis, of the compensation of the Company’s named executive officers (“NEOs”), and “FOR” the approval of the Plan Amendment. It is not expected that any additional matters will be brought before the Annual Meeting, but if other matters are properly presented, the persons named as proxies in the proxy card or their substitutes will vote in their discretion on such matters.

Voting via the Internet, mobile device, or by telephone helps save money by reducing postage and proxy tabulation costs. To vote by any of these methods, read this Proxy Statement, have your Notice of Internet Availability of Proxy Materials, proxy card, or voting instruction form in hand, and follow the instructions below for your preferred method of voting. We believe that each of these voting methods is available 24 hours per day, seven days per week, but you should review your proxy card or voting instruction form for details regarding casting your vote.

We encourage you to cast your vote by one of the following methods, depending on how your shares are held:

•You can use the Internet to vote your proxy athttps://www.cstproxy.com/hyliion/2026. Have your proxy card or voting instruction form available when you access the website. Follow the prompts to vote your shares.

•You can vote at the Annual Meeting by using your 12-digit control number to vote electronically.

•You can mark, sign and date your proxy card or voting instruction form and return it in advance of the meeting.

•You can instruct your bank, brokerage firm, or other nominee how to vote your shares, as further described in “Shares Held in Street Name” below.

Holders of Record. The manner in which your shares may be voted depends on how your shares are held. If you own shares of record, meaning that your shares are represented by certificates or book entries in your name so that you appear as a stockholder on the records of Continental Stock Transfer & Trust Company, our stock transfer agent, you may vote by proxy, meaning you authorize individuals named in the proxy card to vote your shares. You may provide this authorization by voting via the Internet, mobile device, by telephone, or (if you have received paper copies of our proxy materials) by returning a proxy card. You also may participate in and vote during the Annual Meeting, as described in greater detail below. If you own common stock of record and you do not vote by proxy or at the Annual Meeting, your shares will not be voted.

Shares Held in Street Name. If you own shares in street name, meaning that your shares are held by a bank, brokerage firm, or other nominee, you may instruct that institution on how to vote your shares. You generally may provide these instructions by voting via the Internet, mobile device, by telephone, or (if you have received paper copies of proxy materials through your bank, brokerage firm, or other nominee) by returning a voting instruction form received from that institution. You also generally may participate in and vote during the Annual Meeting, as described in greater detail below.

If you own common stock in street name and do not either provide voting instructions or vote during the Annual Meeting, the institution that holds your shares may or may not vote your shares in its discretion. Whether the bank, brokerage firm or other nominee may vote your shares depends on the proposals before the Annual Meeting.

Brokers have the discretionary authority under the rules of the NYSE American, to vote shares for which their clients do not provide voting instructions on certain “routine” matters. The rules of the NYSE American, however, do not permit your bank, broker or other nominee to vote your shares on proposals that are not considered “routine.” When a proposal is not a routine matter and your bank, broker or other nominee has not received your voting instructions with respect to such proposal, your bank, broker or other nominee cannot vote your shares on such proposal. Where brokers do not have discretion to vote or do not exercise such discretion, the inability or failure to vote is referred to as a “broker non-vote.” Under circumstances where a broker is not permitted to exercise its discretion, broker non-votes will not be counted as voting in favor of or against the particular matter.

Please note that your bank, broker or other nominee may not vote your shares with respect to the following matters in the absence of your specific instructions as to how to vote with respect to such matters: (i) the election of the three nominees for director, (ii) the approval, on a non-binding advisory basis, of compensation of our NEOs, or (iii) the approval of the Plan Amendment. Under the rules of the NYSE American, these matters are not considered “routine” matters.

Based on NYSE American rules, we believe that the ratification of the appointment of Grant Thornton LLP as our independent auditors for the fiscal year ended December 31, 2026 is a “routine” matter for which your bank, broker or other nominee may vote on behalf of their clients if no voting instructions are provided. Therefore, if you are a street name shareholder and you do not return your voting instruction card, your bank, broker or other nominee may vote your shares on the ratification of the appointment of Grant Thornton LLP as our independent registered public accounting firm.