Sec Form 3 Filing - Mastrangelo Joe @ Eos Energy Enterprises, Inc. - 2020-11-16

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Mastrangelo Joe 2. Issuer Name and Ticker or Trading Symbol Eos Energy Enterprises, Inc. [ EOSE] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Executive Officer (Last) (First) (Middle) C/O EOS ENERGY ENTERPRISES, INC., 3920 PARK AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 11/16/2020 (Street) EDISON, NJ08820 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Stock Units $ 0 ( 1 ) ( 2 ) Common Stock 74,531 D Options $ 8.67 ( 3 ) 10/23/2030 Common Stock 1,037,484 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Mastrangelo Joe C/O EOS ENERGY ENTERPRISES, INC. 3920 PARK AVENUE EDISON, NJ08820 X Chief Executive Officer Signatures /s/ Joe Mastrangelo 11/23/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The reporting person received restricted stock units which vest in full when the per share price of the Company's common stock quals or exceeds $12.00 at any time. ( 2 )Not applicable ( 3 )Beginning on 10/23/2020, so long as the reporting person remains in service, 691,691 of the shares of common stock subject to this option will vest as to 33.33% on each of the first three anniversaries of June 22, 2020; provided, that such shares shall vest in full upon the consummation of a change in control of the Company. The remaining number of shares subject to this option will vest, provided that the reporting person remains in service, on the day the Board determines that the Company has successfully closed an equity financing transaction prior to June 22, 2023. If no such transaction is consummated by June 22, 2023, any unvested portion of the option shall imeediately terminate.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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