[Form 4] Hyliion Holdings Corp. Insider Trading Activity

Rhea-AI Filing Summary

Hyliion Holdings Corp. officer reports tax-related share transactions. The company’s Chief Technology Officer reported multiple transactions in Hyliion common stock in mid-November 2025. On November 13, 2025, 4,110 shares were withheld at prices of $1.68 per share, and on November 14, 2025, 7,397 shares were withheld at $1.70 per share, both to cover tax liabilities tied to restricted stock unit vesting. On November 17, 2025, 9,039 shares were sold at $1.66 per share under the issuer’s award agreement to satisfy additional tax withholding obligations. After these transactions, the reporting person held 507,572 shares directly. The filing notes that the November 17 sale also corrected an earlier administrative error by a third-party service provider related to tax withholding for shares that vested on August 25, 2025.

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

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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)
11/13/2025

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	11/13/2025		F(1)		4,110	D	$1.68	524,008	D
Common Stock	11/14/2025		F(1)		7,397	D	$1.7	516,611	D
Common Stock	11/17/2025		J(2)(3)		9,039	D	$1.66	507,572	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.

2. These shares were sold at the direction of the issuer under the terms of the issuer's award agreement with the reporting person. Under the award agreement, the decision to sell shares to cover the reporting person's tax withholding obligations is at the sole discretion of the issuer.

3. This transaction includes the sale of issuer common shares to cover the reporting person's tax withholding obligation for vesting dates on August 25, 2025. As a result of an administrative error by the issuer's third-party service provider, cash was paid on behalf of the reporting person for tax withholding obligations on the vesting date, August 25, 2025. A corresponding sale of issuer common shares to cover the reporting person's tax withholding obligation on August 25, 2025 could not be completed until the opening of the issuer's next window period. Accordingly, the the above shares attributed to the vesting on August 25, 2025 were sold November 17, 2025, the first available date during an open window period on which the shares could be sold on behalf of the reporting person.

Remarks:

	/s/ Joshua T. Mook	11/17/2025
	** 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 insider activity did Hyliion (HYLN) report in this Form 4?

The Form 4 reports that Hyliion’s Chief Technology Officer completed several common stock transactions in November 2025, mainly to cover tax withholding obligations related to vested restricted stock units.

How many Hyliion (HYLN) shares did the officer sell or have withheld for taxes?

The officer had 4,110 shares withheld on November 13, 2025, 7,397 shares withheld on November 14, 2025, and 9,039 shares sold on November 17, 2025, all tied to tax withholding obligations.

What were the transaction prices for the Hyliion (HYLN) insider trades?

The reported prices were $1.68 per share on November 13, 2025, $1.70 per share on November 14, 2025, and $1.66 per share on November 17, 2025.

Why were Hyliion (HYLN) shares sold by the officer on November 17, 2025?

The November 17, 2025 sale of 9,039 shares was made at the direction of the issuer under an award agreement to cover the officer’s tax withholding obligations, including amounts tied to shares that vested on August 25, 2025.

Did Hyliion’s reporting person still own shares after these Form 4 transactions?

Yes. After the reported transactions, the reporting person beneficially owned 507,572 shares of Hyliion common stock directly.

What administrative error is described in the Hyliion (HYLN) Form 4 footnotes?

The filing states that, due to an error by a third-party service provider, cash was initially used to pay tax withholding for shares that vested on August 25, 2025, and the related share sale to cover those taxes occurred later, on November 17, 2025, during the next open trading window.