Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

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

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(Print or Type Responses)

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 (Month/Day/Year) 06/12/2026 (Street) EDISON, NJ 08820 4. If Amendment, Date Original Filed (Month/Day/Year) 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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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 Common Stock 06/12/2026 M 200,000 A $1.34 1,687,126 D Common Stock 06/12/2026 F 116,646(1) D $6.06 1,570,480 D

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

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 (Month/Day/Year)

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

Stock Option (Right to Buy)

$1.34

06/12/2026

M

200,000

(2)

06/16/2032

Common Stock

200,000

$ 0

0

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, NJ 08820	X		Chief Executive Officer

Signatures

/s/ Michael Silberman as attorney-in-fact for Joe Mastrangelo		06/15/2026
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	The transactions reported in this Form 4 reflect the exercise of Non-Qualified Stock Options by the Reporting Person and the subsequent retention of the underlying shares of Common Stock. The option exercise and corresponding acquisition of shares reported in Table I and Table II were exempted from Section 16(b) liability pursuant to Rule 16b-3 promulgated under the Securities Exchange Act of 1934. The Reporting Person has elected to retain the net shares acquired upon exercise to maintain and support their long-term equity position in the Issuer, including in connection with any potential future equity or rights offerings that may be conducted by the Issuer.
(2)	On June 16, 2022 the reporting person was granted stock options to purchase 200,000 shares of common stock which vested on September 27, 2022.

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