[Form 4] Hyliion Holdings Corp. Insider Trading Activity

Rhea-AI Filing Summary

Joshua T. Mook, Chief Technology Officer of Hyliion Holdings Corp. (HYLN), reported a non-derivative disposition of common stock on 08/27/2025. The filing shows 1,361 shares were disposed of at $1.69 per share, leaving the reporting person with 519,688 shares beneficially owned after the transaction. The explanatory note states the shares were withheld to satisfy a tax liability related to the vesting and distribution of restricted stock units. The Form 4 is signed by Joshua T. Mook on 08/29/2025 and identifies the transaction as routine withholding for taxes rather than an open-market sale.

Insights

Financial Analyst

TL;DR: Small tax-withholding share disposition; ownership remains substantial, so limited market impact.

The reported transaction is a routine withholding of 1,361 shares at $1.69 to cover taxes tied to RSU vesting, leaving 519,688 shares beneficially owned. For a corporate insider, such withholding is common and not usually indicative of a change in conviction or liquidity-driven selling. The absolute number disposed is immaterial relative to the residual stake, so this Form 4 is unlikely to affect valuation or signal operational developments.

Corporate Governance Expert

TL;DR: Administrative tax-related withholding disclosed appropriately; governance disclosure requirements satisfied.

The Form 4 discloses the withholding of shares to satisfy tax obligations from RSU distributions, a standard compensation-administration action. The reporting person is properly identified as an officer (CTO) and the filing includes signature and transaction details. From a governance and compliance standpoint, the disclosure appears complete and timely for this type of transaction.

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
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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 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^*

MOOK JOSHUA T.

(Last) (First) (Middle)

C/O HYLIION HOLDING CORP.

1202 BMC DRIVE, SUITE 100

(Street)

CEDAR PARK TX 78613

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Hyliion Holdings Corp. [ HYLN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Technology Officer

3. Date of Earliest Transaction (Month/Day/Year)
08/27/2025

4. If Amendment, Date of 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

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	08/27/2025		F(1)		1,361	D	$1.69	519,688	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

Explanation of Responses:

1. Shares withheld for the payment of a tax liability related to the vesting and distribution of restricted stock units.

Remarks:

	/s/ Joshua T. Mook	08/29/2025
	** 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.

FAQ

What did Joshua T. Mook report on Form 4 for HYLN?

The filing reports a disposition of 1,361 shares at $1.69 per share on 08/27/2025, leaving 519,688 shares beneficially owned.

Why were the 1,361 shares disposed of according to the Form 4?

The explanation states the shares were withheld to pay a tax liability related to the vesting and distribution of restricted stock units.

What is Joshua T. Mook's role at Hyliion and how is he related to the issuer?

He is reported as the company's Chief Technology Officer and filed the Form 4 as an officer.

When was the Form 4 signed?

The Form 4 is signed by Joshua T. Mook on 08/29/2025.

Does the Form 4 indicate an open-market sale or other transaction type?

The transaction code is F(1), and the explanation identifies it as shares withheld for taxes, not an open-market sale.