Eos Energy CEO sells 250K shares after RSU vesting

Eos Energy’s CEO had 500,000 performance-based RSUs vest and then sold 250,000 shares under a Rule 10b5-1 plan to cover tax obligations.

Rhea-AI Filing Summary

Eos Energy Enterprises, Inc. (EOSE) reported that Chief Executive Officer and director Joe Mastrangelo had performance-based restricted stock units from a 2024 award vest on September 14, 2026, resulting in the delivery of 500,000 shares of common stock tied to total shareholder return performance.

Following this vesting, on September 16, 2026, Mastrangelo sold 250,000 shares of common stock at a weighted average price of $3.92 per share, with sale prices ranging from $3.84 to $4.16, in transactions effected automatically under a Rule 10b5-1 trading plan adopted on September 15, 2025 to cover estimated tax withholding obligations.

Insider Trade Summary 10b5-1

Exercise and sale activity reported; no spread calculated

Exercise and Sale 3 txns

Insider Mastrangelo Joe

Role Chief Executive Officer

Sold 250,000 shs ($980K)

Approx. gross sale proceeds $980K

Type	Security	Shares	Price	Value
Sale	Common Stock F2, F3	250,000	$3.92	$980K
Exercise	Performance-Based Restricted Stock Units F1, F4, F5	500,000	$0.00	$0.00
Grant/Award	Common Stock F1	500,000	$0.00	$0.00

Holdings After Transaction: Performance-Based Restricted Stock Units — 0 contracts (Direct); Common Stock — 2,308,704 shares (Direct)

Footnotes (5)

1. 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.
2. 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.
3. 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.
4. 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.
5. F5. Not applicable.

Key Figures

Common shares sold: 250,000 shares Weighted average sale price: $3.92 per share Sale price range: $3.84–$4.16 per share +4 more

7 metrics

Common shares sold 250,000 shares Shares of Eos Energy common stock sold by CEO on September 16, 2026

Weighted average sale price $3.92 per share Weighted average price for the 250,000 shares sold on September 16, 2026

Sale price range $3.84–$4.16 per share Range of prices for the multiple transactions included in the 250,000-share sale

Vested shares from 2024 PRSU Awards 500,000 shares Common shares delivered upon vesting of performance-based RSUs on September 14, 2026

2024 PRSU performance periods 2 and 3 years Performance periods for total shareholder return starting July 5, 2024

Rule 10b5-1 plan adoption date September 15, 2025 Date CEO adopted trading plan used for the 250,000-share sale

Remaining 2024 PRSU units reported 0 units Outstanding units from the reported 2024 PRSU award after the September 14, 2026 conversion

Key Terms

Rule 10b5-1 trading plan, performance-based restricted stock units, total shareholder return, vesting, +1 more

5 terms

Rule 10b5-1 trading plan regulatory

"sales were effected automatically pursuant to a Rule 10b5-1 trading plan"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

performance-based restricted stock units financial

"the Reporting Person was granted performance-based restricted stock units"

Performance-based restricted stock units are a type of employee equity award that converts into company shares only if predefined financial or operational targets are met over a set period. Think of it like a bonus check that becomes stock only when specific goals are hit; it ties pay to results, aligning managers’ incentives with shareholders. Investors care because these awards affect future share count, executive incentives, and signal how management’s success will be measured and rewarded.

total shareholder return financial

"eligible to vest based on the total shareholder return of the Issuer"

Total shareholder return is the overall gain an investor gets from owning a stock, combining changes in the share price plus any cash payouts like dividends, and assuming those payouts are reinvested in more shares. Investors use it like a single score that shows the true return on their investment—similar to checking both the growth of a savings account and the interest earned—to compare how well different companies or investments perform over time.

vesting financial

"certified the achievement of the first performance period, resulting in the vesting"

Vesting is the process by which you earn full ownership of something, like company stock or a retirement benefit, over time. It’s like earning the right to keep a gift piece by piece the longer you stay with a company, making sure employees stay committed before they receive all the benefits.

weighted average price financial

"The price reported in Column 4 is a weighted average price"

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transactions did EOSE report for CEO Joe Mastrangelo?

Eos Energy reported that CEO Joe Mastrangelo had 500,000 performance-based RSUs vest into common stock on September 14, 2026, and then sold 250,000 common shares on September 16, 2026 under a pre-arranged Rule 10b5-1 trading plan.

How many EOSE shares did the CEO sell and at what price?

Joe Mastrangelo sold 250,000 shares of Eos Energy common stock on September 16, 2026 at a weighted average price of $3.92 per share, with individual trade prices ranging from $3.84 to $4.16.

Were the September 2026 EOSE CEO stock sales under a Rule 10b5-1 plan?

Yes. The filing states that the 250,000-share sale on September 16, 2026 was effected automatically under a Rule 10b5-1 trading plan adopted by Joe Mastrangelo on September 15, 2025 to cover estimated tax withholding obligations.

What performance-based RSUs vested for the EOSE CEO in September 2026?

On September 14, 2026, the Compensation Committee certified achievement of the first performance period of 2024 performance-based RSU awards, resulting in the vesting and delivery of 500,000 shares of common stock to CEO Joe Mastrangelo.

What are the performance conditions on EOSE’s 2024 PRSU awards to the CEO?

The 2024 performance-based restricted stock unit awards are eligible to vest in up to two installments based on total shareholder return over two- and three-year performance periods, each commencing on July 5, 2024.

Does the Form 4 show any remaining 2024 PRSU units for the EOSE CEO?

The derivative transaction table shows 500,000 performance-based RSUs related to the 2024 award being exercised or converted, with 0 units remaining from that reported award after the transaction.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/16/2026 - 04:27 PM Accepted by SEC EDGAR 09/16/2026 - 04:27 PM Learn about SEC filing dates

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Mastrangelo Joe

(Last) (First) (Middle)

C/O EOS ENERGY ENTERPRISES, INC.

TWO ALLEGHENY CENTER, NOVA TOWER 2

(Street)

PITTSBURGH PENNSYLVANIA 15212

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/14/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

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	09/14/2026		A		500,000	A	$0(1)	2,558,704	D
Common Stock	09/16/2026		S(2)		250,000	D	$3.92(3)	2,308,704	D

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 Securities Underlying Derivative Security (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: 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
Performance-Based Restricted Stock Units(1)	(1)	09/14/2026		M			500,000(4)	(5)	(5)	Common Stock	500,000	$0	0	D

Explanation of Responses:

1. 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.

2. 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.

3. 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.

4. 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.

5. Not applicable.

Remarks:

	/s/ Sumeet Puri as attorney-in-fact for Joe Mastrangelo	09/16/2026
	** Signature of Reporting Person	Date
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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)