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☑ ப ☐ UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , DC 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 ог TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period from Delaware ( State or Other Jurisdiction of Incorporation or Organization ) Title of Each Class Common Stock , $ 0.001 Par Value to Commission File Number : 001-35005 ASSEMBLY BIOSCIENCES , INC . ( Exact name of registrant specified in its charter ) 331 Oyster Point Blvd. , Fourth Floor South San Francisco , California 94080 ( Address of Principal Executive Offices ) Registrant's telephone number , including area code : ( 833 ) 509-4583 Securities Registered Pursuant to Section 12 ( b ) of the Exchange Act : Trading Symbol ( s ) ASMB Securities Registered Pursuant to Section 12 ( g ) of the Act : None 20-8729264 ( I.R.S. Employer Identification No. ) Name of Exchange on which Registered The Nasdaq Global Select Market Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes ☐ No ☑ Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange Act . Yes □ No ☑ 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 > No ☐ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.45 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes > No ☐ 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 the definitions 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 ☑ Accelerated filer Smaller reporting company Emerging growth company ☐ П ☐ 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 . 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 the voting stock held by non - affiliates of the registrant , as of June 30 , 2020 , was $ 756.9 million . Such aggregate market value was computed by reference to the closing price of the common stock as reported on the Nasdaq Global Select Market on June 30 , 2020. For purposes of making this calculation only , the registrant has defined affiliates as including only ( 1 ) directors , ( 2 ) executive officers and ( 3 ) certain stockholders , if any , that hold greater than 10 % of the voting stock of the registrant , in each case , as of June 30 , 2020. Shares of common stock held by other persons , including certain other holders of more than 10 % of the registrant's outstanding common stock , if any , have not been excluded from the above calculation in that such persons are not deemed to be affiliates . The determination of affiliate status is not necessarily a conclusive determination for other purposes . As of February 22 , 2021 , there were 38,246,092 shares of the registrant's common stock , $ 0.001 par value per share , outstanding . DOCUMENTS INCORPORATED BY REFERENCE Part III of this Annual Report on Form 10 - K incorporates information by reference to portions of the definitive proxy statement for the Company's Annual Meeting of Stockholders to be held in 2021 , to be filed within 120 days of the registrant's fiscal year ended December 31 , 2020 .