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☑ ☐ 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 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number : 001-38796 GOSSAMER BIO , INC . ( Exact name of Registrant as specified in its charter ) 47-5461709 ( I.R.S. Employer Identification No. ) Delaware ( State or other jurisdiction of incorporation or organization ) 3013 Science Park Road San Diego , California ( Address of principal executive offices ) Registrant's telephone number , including area code : ( 858 ) 684-1300 Title of each class 92121 ( Zip Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) GOSS Name of each exchange on which registered Nasdaq Global Select Market Common Stock , $ 0.0001 par value per share Securities registered pursuant to Section 12 ( g ) of the Act : None 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 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 ( § 232.405 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 Securities Exchange Act of 1934 . Large accelerated filer Non - accelerated filer Emerging growth company ☐ ㅁ Accelerated filer Smaller reporting 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 . 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 As of June 30 , 2020 ( the last business day of the registrant's most recently completed second fiscal quarter ) , the aggregate market value of the registrant's common stock held by non - affiliates of the registrant was approximately $ 774.8 million , based on the closing price of the registrant's common stock on the Nasdaq Global Select Market of $ 13.00 per share . As of February 19 , 2021 , the registrant had 75,527,707 shares of common stock ( $ 0.0001 par value ) outstanding . DOCUMENTS INCORPORATED BY REFERENCE Certain sections of the registrant's definitive proxy statement for the 2021 annual meeting of stockholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after end of this fiscal year covered by this Form 10 - K are incorporated by reference into Part III of this Form 10 - K .