Eos Energy Enterprises, Inc. (EOSE)

=== SEC Form 4 — Statement of Changes in Beneficial Ownership === Document Type: 4 Period of Report: 2026-09-14 10b5-1 Pre-arranged Plan: Yes --- Issuer --- Name: Eos Energy Enterprises, Inc. (EOSE) CIK: 0001805077 --- Reporting Owner --- Name: Mastrangelo Joe CIK: 0001833309 Role: Director, Officer (Chief Executive Officer) --- Non-Derivative Transactions --- [Transaction #1] Security: Common Stock Date: 2026-09-14 | Code: A (Grant or award) Shares: +500,000 | Price: $0.00 Shares Owned After: 2,558,704 | Ownership: D (Direct) Footnotes: [F1] On July 5, 2024, the Reporting Person was granted performance-based restricted stock units ("2024 PRSU Awards"). The 2024 PRSU Awards are eligible to vest in up to two installments based on the total shareholder return of the Issuer over two- and three-year performance periods, each commencing on July 5, 2024. On September 14, 2026, the Compensation Committee of the Issuer's Board of Directors certified the achievement of the first performance period, resulting in the vesting of these shares. [Transaction #2] Security: Common Stock Date: 2026-09-16 | Code: S (Open market sale) Shares: -250,000 | Price: $3.92 Total Value: $980,000.00 Shares Owned After: 2,308,704 | Ownership: D (Direct) Footnotes: [F2] The sales reported in this Form 4 were effected automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on September 15, 2025 to cover estimated tax withholding obligations in connection with the vesting of performance-based restricted stock units. [F3] The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $3.84 to $4.16, inclusive. The reporting person undertakes to provide the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above. --- Derivative Transactions --- [Transaction #1] Security: Performance-Based Restricted Stock Units Date: 2026-09-14 | Code: M (Exercise of derivative) Shares: -500,000 | Price: $0.00 Shares Owned After: 0 | Ownership: D (Direct) Footnotes: [F1] On July 5, 2024, the Reporting Person was granted performance-based restricted stock units ("2024 PRSU Awards"). The 2024 PRSU Awards are eligible to vest in up to two installments based on the total shareholder return of the Issuer over two- and three-year performance periods, each commencing on July 5, 2024. On September 14, 2026, the Compensation Committee of the Issuer's Board of Directors certified the achievement of the first performance period, resulting in the vesting of these shares. [F1] On July 5, 2024, the Reporting Person was granted performance-based restricted stock units ("2024 PRSU Awards"). The 2024 PRSU Awards are eligible to vest in up to two installments based on the total shareholder return of the Issuer over two- and three-year performance periods, each commencing on July 5, 2024. On September 14, 2026, the Compensation Committee of the Issuer's Board of Directors certified the achievement of the first performance period, resulting in the vesting of these shares. [F4] Represents the outstanding awarded and vested units pursuant to the 2024 PRSU Awards dated July 25, 2024 related to the achievement of certain total shareholder return objectives. [F5] Not applicable. [F5] Not applicable. --- Footnotes (Complete Index) --- F1: On July 5, 2024, the Reporting Person was granted performance-based restricted stock units ("2024 PRSU Awards"). The 2024 PRSU Awards are eligible to vest in up to two installments based on the total shareholder return of the Issuer over two- and three-year performance periods, each commencing on July 5, 2024. On September 14, 2026, the Compensation Committee of the Issuer's Board of Directors certified the achievement of the first performance period, resulting in the vesting of these shares. F2: The sales reported in this Form 4 were effected automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on September 15, 2025 to cover estimated tax withholding obligations in connection with the vesting of performance-based restricted stock units. F3: The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $3.84 to $4.16, inclusive. The reporting person undertakes to provide the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above. F4: Represents the outstanding awarded and vested units pursuant to the 2024 PRSU Awards dated July 25, 2024 related to the achievement of certain total shareholder return objectives. F5: Not applicable. --- Signature --- /s/ /s/ Sumeet Puri as attorney-in-fact for Joe Mastrangelo (2026-09-16)