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Table of Contents ( Mark One ) UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR Title of each class Common Stock , $ 0.001 par value For the transition period from to Commission File Number : 001-36383 Delaware ( State or Other Jurisdiction of Incorporation or Organization ) X O Five9 , Inc. ( Exact Name of Registrant as Specified in Its Charter ) 3001 Bishop Drive , Suite 350 San Ramon , CA 94583 Principal Executive Offices ) ( Zip Code ) ( I.R.S. Employer Identification No. ) ( Address of ( 925 ) 201-2000 ( Registrant's Telephone Number , Including Area Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) 94-3394123 FIVN Securities registered pursuant to Section 12 ( g ) of the Act : None Name of each exchange on which registered The NASDAQ Global Market Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes : x No : 0 Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes : o No : x Indicate by check mark whether the registrant : ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes : x No : 0 submitted pursuant to Indicate by chec whether the registrant has submitted electronically every Interactive Da File required to 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit and post such files ) . Yes : x No : 0 Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See definition of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large Accelerated Filer Non - accelerated filer ( Do not check if a smaller reporting Company ) Accelerated Filer Smaller Reporting Company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . O Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . < Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes : □ No : The aggregate market value of registrant's common stock held by non - affiliates of the registrant based upon the closing sale price on the NASDAQ Global Market on June 30 , 2020 , the last business day of the Registrant's most recently completed second fiscal quarter , was approximately $ 5,711.0 million . Shares held by each executive officer , director and their affiliated holders and by each other person ( if any ) who owns 10 % of the outstanding common stock or more have been excluded in that such persons may be deemed to be affiliates . This determination of affiliate status is not necessarily a conclusive determination for other purposes . As of February 19 , 2021 , there were 66,659,859 shares of the Registrant's common stock , par value $ 0.001 per share , outstanding . DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's definitive Proxy Statement for the 2021 Annual Stockholders ' Meeting , which the registrant expects to file with the Securities and Exchange Commission within 120 days of December 31 , 2020 , are incorporated by reference into Part III ( Items 10 , 11 , 12 , 13 and 14 ) of this Annual Report on Form 10 - K .