GARTNER INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Check the appropriate box:

GARTNER, INC.

(Name of Registrant as Specified in Its Charter)

Payment of Filing Fee (Check all boxes that apply):

Dear Stockholder:

On behalf of the Board of Directors and Management of Gartner, Inc., you are invited to attend our 2026 Annual Meeting of Stockholders to be held on Thursday, May 28, 2026, at 10 a.m. Eastern Time, via live audio webcast over the internet atwww.virtualshareholdermeeting.com/IT2026. Stockholders or their legal proxy holders can participate, submit questions, and vote at the Annual Meeting by visitingwww.virtualshareholdermeeting.com/IT2026 and using a valid control number. As always, we encourage you to vote your shares prior to the Annual Meeting.

Details of the business to be conducted at the meeting are given in the Notice of Annual Meeting of Stockholders and Proxy Statement which follow this letter. The 2025 Annual Report to Stockholders is also included with these materials.

We have mailed to many of our stockholders a Notice of Internet Availability of Proxy Materials (the “Notice”) containing instructions on how to access our 2026 Proxy Statement and our 2025 Annual Report to Stockholders, and how to vote online on the three management Proposals put before you this year. The Notice also includes instructions on how to request a paper or email copy of the proxy materials, including the Notice of Annual Meeting, Proxy Statement and Annual Report, and proxy card or voting instruction card. Stockholders who previously either requested paper copies of the proxy materials or elected to receive the proxy materials electronically did not receive a Notice and will receive the proxy materials in the format requested.

In addition, by following the e-consent instructions in the proxy card, stockholders may go paperless in future solicitations and request proxy materials electronically by email on an ongoing basis.

Your vote is important. Whether or not you plan to attend the Annual Meeting, we urge you to review the proxy materials and vote your shares, regardless of the number of shares you hold, as soon as possible. You may vote by proxy over the internet or by telephone using the instructions provided in the Notice. Alternatively, if you received paper copies of the proxy materials by mail, you can also vote by following the instructions on the proxy card or voting instruction card. Instructions regarding the three methods of voting are contained in the Notice, proxy card or voting instruction card.

If you have any questions about the meeting, please contact our Investor Relations Department at investor.relations@gartner.com.

Sincerely,

Eugene A. Hall

Chairman of the Board and Chief Executive Officer

2026 Proxy Statement

56 Top Gallant Road

Stamford, Connecticut 06902

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

To be admitted to the Annual Meeting, please visitwww.virtualshareholdermeeting.com/IT2026. Online check-in will be available approximately 15 minutes before the meeting starts. Stockholders of record as of the close of business on April 2, 2026, the Record Date, are entitled to participate in and vote at the Annual Meeting. To participate in the Annual Meeting, including to vote and ask questions during the Annual Meeting, stockholders of record should go to the meeting website atwww.virtualshareholdermeeting.com/IT2026, enter the 16-digit control number found on your proxy card or Notice of Internet Availability of Proxy Materials (the “Notice”), and follow the instructions on the website. If your shares are held in street name and your voting instruction form or Notice indicates that you may vote those shares through the http://www.proxyvote.com website, then you may access, participate in, and vote at the annual meeting with the 16-digit access code indicated on that voting instruction form or Notice. Otherwise, stockholders who hold their shares in street name should contact their bank, broker or other nominee (preferably at least 5 days before the Annual Meeting) and obtain a “legal proxy” in order to be able to attend, participate in or vote at the Annual Meeting. For more information about how to attend the Annual Meeting online, please see “Information Concerning Proxy Materials and the Voting of Proxies –How Can I Participate in the 2026 Annual Stockholders’ Meeting?” on page 61 of the Proxy Statement.

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting of Stockholders to Be Held on May 28, 2026: We are making this Notice of Annual Meeting, this Proxy Statement and our 2025 Annual Report available on the Internet atwww.proxyvote.com and mailing copies of these Proxy Materials to certain stockholders on or about April 15, 2026.

By Order of the Board of Directors,

Thomas Kim

Executive Vice President, Chief Legal Officer & Secretary

Stamford, Connecticut

2026 Proxy Statement

TABLE OF CONTENTS

2026 Proxy Statement