Vertex, Inc.

CEO Pay R

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934

VERTEX, INC.

(Name of Registrant as Specified in its Charter)

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ 800.355.3500 vertexinc.com​​​

​​​​April 27, 2026​To Our Stockholders:​You are cordially invited to attend the 2026 Annual Meeting of Stockholders of Vertex, Inc. (the "Company") to be held on June 10, 2026. Our Annual Meeting will be a completely virtual meeting of stockholders, which will be conducted via live webcast. You will be able to attend the virtual Annual Meeting, vote your shares electronically and submit your questions during the meeting. Utilizing the latest technology and a virtual meeting format will allow stockholders to participate from any location, and which we expect will lead to increased attendance, improved communications and cost savings for our stockholders and the Company.​The Notice of Annual Meeting and Proxy Statement on the following pages describe the matters to be presented at the Annual Meeting. Details regarding how to attend the meeting and the business to be conducted at the Annual Meeting are more fully described in the Notice of Annual Meeting and Proxy Statement.​Whether or not you attend the Annual Meeting, it is important that your shares be represented and voted at the Annual Meeting. Therefore, I urge you to promptly vote and submit your proxy by phone, via the Internet, or, if you requested to receive paper copies of these materials, by signing, dating, and returning the enclosed proxy card in the enclosed envelope, which requires no postage if mailed in the United States. If you have previously received our Notice of Internet Availability of Proxy Materials, then instructions regarding how you can vote are contained in that notice. If you have requested to receive a proxy card, then instructions regarding how you can vote are contained on the proxy card. If you decide to attend the Annual Meeting, you will be able to vote your shares electronically, even if you have previously submitted your proxy.​Thank you for your support.​Sincerely,​/s/ Christopher Young​​Christopher YoungPresident and Chief Executive Officer ​​​​​​​​​​2301 Renaissance Blvd, King of Prussia, PA 19406T: 800.355.3500 vertexinc.com​​​

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Notice of

2026 Annual Meeting of Stockholders

TO THE STOCKHOLDERS OF VERTEX, INC.

NOTICE IS HEREBY GIVEN that the 2026 Annual Meeting of Stockholders (the "Annual Meeting") of Vertex, Inc., a Delaware corporation (the “Company”), will be a completely virtual meeting, which will be conducted via live webcast at the date and time below:

Wednesday, June 10, 2026

9:00 a.m. EDT

You will be provided with instructions on registering and attending the virtual meeting as well as voting prior to and during the meeting. The Annual Meeting is called for the following purposes:

Holders of record of our outstanding shares of capital stock, composed of Class A Common Stock and Class B Common Stock (collectively, “Common Stock”), at the close of business on April 15, 2026, are entitled to notice of and to vote at the Annual Meeting, or any continuation, postponement or adjournment of the Annual Meeting. A complete list of these stockholders will be available for examination by any stockholder during the ten (10) days prior to the Annual Meeting for a purpose germane to the meeting by sending an email to legal@vertexinc.com, stating the purpose of the request and providing proof of ownership of Company stock. This list of stockholders will also be available on the bottom panel of your screen during the meeting after entering the appropriate password included on the Notice of Internet Availability of Proxy Materials or any proxy card that you received, or on the materials provided by your bank or broker. The Annual Meeting may be continued or adjourned from time to time without notice other than by announcement at the Annual Meeting.

IT IS IMPORTANT THAT YOUR SHARES BE REPRESENTED, REGARDLESS OF THE NUMBER OF SHARES YOU MAY HOLD. WHETHER OR NOT YOU PLAN TO ATTEND THE ANNUAL MEETING, WE URGE YOU TO VOTE YOUR SHARES VIA THE TELEPHONE NUMBER OR OVER THE INTERNET, AS DESCRIBED IN THE ENCLOSED MATERIALS. IF YOU REQUESTED TO RECEIVE A COPY OF THE PROXY CARD BY MAIL, YOU MAY SIGN, DATE AND MAIL THE PROXY CARD IN THE ENCLOSED RETURN ENVELOPE. PROMPTLY VOTING YOUR SHARES WILL ENSURE THE PRESENCE OF A QUORUM AT THE ANNUAL MEETING AND WILL SAVE US THE EXPENSE OF FURTHER SOLICITATION. SUBMITTING YOUR PROXY NOW WILL NOT PREVENT YOU FROM VOTING YOUR SHARES AT THE ANNUAL MEETING IF YOU DESIRE TO DO SO, AS YOUR PROXY IS REVOCABLE AT YOUR OPTION.

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By Order of the Board of Directors

/s/ John Schwab

John Schwab

Chief Financial Officer

King of Prussia, PA

April 27, 2026

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Proxy S****ummary

This summary highlights important information regarding the Annual Meeting and the Proxy Statement. It does not cover all of the information you should consider before voting, and you are encouraged to read the entire Proxy Statement before casting your vote.

Corporate Website: www.vertexinc.com

Investor Relations Website: ir.vertexinc.com

The information found on, or otherwise accessible through, our website is not incorporated by reference into, nor does it form a part of, this Proxy Statement.

RECOMMENDATIONS OF THE BOARD

The Company’s Board of Directors (the “Board”) recommends that you vote your shares as indicated below. If you return a properly completed proxy card, or vote your shares by telephone or Internet, your shares of Common Stock will be voted on your behalf as you direct. If not otherwise specified, the shares of Common Stock represented by the proxies will be voted, and the Board recommends that you vote:

FOR the election of three Directors: Eric Andersen, David DeStefano and Christopher Young.** **

FOR the ratification of the appointment of Crowe LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2026.

WHY YOU RECEIVED THIS PROXY STATEMENT.

You are viewing or have received these proxy materials because the Board is soliciting your proxy to vote your shares at the Annual Meeting. This Proxy Statement includes information that we are required to provide to you under the rules of the Securities and Exchange Commission and that is designed to assist you in voting your shares.

PRINTED COPIES OF OUR PROXY MATERIALS.

If you received printed copies of our proxy materials, then instructions regarding how you can vote are contained on the proxy card included in the materials.

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