Five9, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 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

(Amendment No. )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

Five9, Inc.

(Name of Registrant as Specified In Its Charter)

n/a

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

FIVE9, INC., 3001 Bishop Drive, Suite 350, San Ramon, CA 94583

Dear Stockholder:

We are pleased to invite you to attend Five9, Inc.’s 2026 Annual Meeting of Stockholders, to be held on May 20, 2026 (the “Annual Meeting”). The meeting will begin promptly at 8:30 a.m. Pacific Daylight Time virtually over the Internet atwww.virtualshareholdermeeting.com/FIVN2026. Instructions on how to participate in the Annual Meeting and demonstrate proof of stock ownership are posted atwww.proxyvote.com. The webcast of the Annual Meeting will be archived for one year after the date of the Annual Meeting atwww.virtualshareholdermeeting.com/FIVN2026. Only stockholders who held stock at the close of business on the record date, March 24, 2026, may vote at the Annual Meeting, including any adjournment or postponement thereof.

Details regarding the business to be conducted at the Annual Meeting are more fully described in the accompanying Notice of Annual Meeting of Stockholders and Proxy Statement. We encourage you to carefully read these materials, as well as our Annual Report to Stockholders.

We are acting under a U.S. Securities and Exchange Commission rule that allows companies to furnish their proxy materials over the Internet rather than in paper form. Consequently, stockholders will not receive paper copies of our proxy materials unless they specifically request them. We believe that this delivery process will reduce our environmental impact and lower the costs of printing and distributing our proxy materials. We believe that we can achieve these benefits with no impact on our stockholders’ timely access to this important information.

Your vote is important. Whether or not you expect to attend the Annual Meeting, please vote by telephone or the Internet according to the instructions on your proxy card or in the Notice of Internet Availability of Proxy Materials (the “Notice”) or request a proxy card from us by email at ir@five9.com and complete, date, sign, and return your proxy card in the envelope provided, in each such case, as soon as possible to ensure that your shares will be represented and voted at the Annual Meeting. Even if you have voted by proxy, you may still vote through our virtual web conference if you attend the Annual Meeting.

On behalf of the Board of Directors, thank you for your continued interest and support.

Sincerely,

FIVE9, INC., 3001 Bishop Drive, Suite 350, San Ramon, CA 94583

Whether or not you expect to attend the Annual Meeting, please vote over the telephone or the Internet as instructed in these materials, or request a proxy card from the Company by email at ir@five9.com and complete, date, sign and return the proxy card in the envelope provided, in each case as promptly as possible in order to ensure your representation at the Annual Meeting. A return envelope (which is postage prepaid if mailed in the United States) will be provided to you if you email a request for a proxy card to the Company atir@five9.com. Even if you have voted by proxy, you may still vote through our virtual web conference if you attend the Annual Meeting. Please note, however, that if your shares are held of record by a broker, bank or other nominee and you wish to vote at the Annual Meeting, you must obtain a proxy issued in your name from that record holder.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON MAY 20, 2026.

The Proxy Statement and Annual Report to Stockholders are available athttp://investors.five9.comand www.proxyvote.com.

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