Vertex, Inc.

Information Concerning Voting and Solicitation

This Proxy Statement is furnished in connection with the solicitation by the Board of Directors of Vertex, Inc. (the “Board”) of proxies to be voted at our Annual Meeting of Stockholders to be held on June 10, 2026 (the "Annual Meeting"), at 9:00 a.m. EDT, and at any continuation, postponement, or adjournment of the Annual Meeting. The Annual Meeting will be a completely virtual meeting, which will be conducted via live webcast. In order to attend the Annual Meeting, you must register at www.proxydocs.com/verx. Upon completing your registration, you will receive further instructions via email, including a unique link that will allow you access to the Annual Meeting and to vote and submit questions during the Annual Meeting. As part of the registration process, you must enter the control number located on your proxy card, voting instruction form, or Notice of Internet Availability. If you are a beneficial owner of shares registered in the name of a broker, bank or other nominee, you will also need to provide the registered name on your account and the name of your broker, bank or other nominee as part of the registration process.

Holders of record of outstanding shares of capital stock, composed of Class A Common Stock and Class B Common Stock, at the close of business on April 15, 2026 (the "Record Date"), will be entitled to notice of and to vote at the Annual Meeting and any continuation, postponement, or adjournment of the Annual Meeting, and will vote together as a single class on all matters presented at the Annual Meeting. Each share of our Class A Common Stock entitles its holders to one vote per share on all matters presented to our stockholders at the Annual Meeting. Our Class B Common Stock entitles its holders to ten (10) votes per share on all matters presented to a vote of our stockholders at the Annual Meeting. At the close of business on the Record Date, there were 79,582,144 shares of Class A Common Stock, and 82,155,641 shares of Class B Common Stock issued and outstanding and entitled to vote at the Annual Meeting, representing 8.8% and 91.2% of the combined voting power of our Common Stock, respectively.

This Proxy Statement will be released on or about April 27, 2026 to our stockholders on the Record Date.

In this Proxy Statement, "we," "us," "our," the "Company," and "Vertex" refer to Vertex, Inc., and, unless otherwise stated, all of its subsidiaries.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON WEDNESDAY, JUNE 10, 2026.

This Proxy Statement is available at www.proxydocs.com/verx.

Why you received the Notice of Internet Availability of this Proxy Statement. You are viewing or have received these proxy materials because Vertex’s 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 (the "SEC") 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.