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Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( Mark one ) 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 Delaware ( State or other jurisdiction of incorporation ) TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to EOS ENERGY ENTERPRISES , INC . ( Exact name of registrant as specified in its charter ) 001-39291 ( Commission File Number ) 3920 Park Avenue Edison , New Jersey 08820 ( Address of principal executive offices , including zip code ) Registrant's telephone number , including area code : ( 732 ) 225-8400 Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) EOSE EOSEW 84-4290188 ( IRS Employer Identification No. ) Name of each exchange on which registered The Nasdaq Stock Market LLC The Nasdaq Stock Market LLC Title of each class Common stock , par value $ 0.0001 per share Warrants , each exercisable for one share of common stock 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 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 the " large accelerated filer , " " accelerated filer , " " non - accelerated filer , " " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act .