Hyliion Holdings Corp. (HYLN) CTO reports 12,949-share tax withholding sale

Rhea-AI Filing Summary

Hyliion Holdings Corp. Chief Technology Officer Joshua T. Mook reported an insider transaction involving the company’s common stock. On 12/12/2025, 12,949 shares were disposed of at $1.94 per share, leaving 1,033,803 shares beneficially owned afterward in direct form.

The filing explains that these shares were sold at the direction of the issuer under the terms of an award agreement to cover Mook’s tax withholding obligations, with the issuer holding sole discretion over whether to sell shares for this purpose.

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)
12/12/2025

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	12/12/2025		J(1)		12,949	D	$1.94	1,033,803	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. 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.

Remarks:

	/s/ Joshua T. Mook	12/15/2025
	** 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).
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FAQ

Who filed this insider transaction related to Hyliion Holdings Corp. (HYLN)?

The transaction was reported by Joshua T. Mook, who serves as Chief Technology Officer of Hyliion Holdings Corp., as indicated in the filing.

What type of Hyliion (HYLN) security was involved and on what date did the transaction occur?

The transaction involved Hyliion Holdings Corp. common stock, and it took place on 12/12/2025, according to the reported transaction date.

How many Hyliion (HYLN) shares did the CTO dispose of and at what price?

The Chief Technology Officer disposed of 12,949 shares of Hyliion common stock at a price of $1.94 per share, as shown in Table I of the filing.

How many Hyliion (HYLN) shares does the reporting person beneficially own after this transaction?

Following the reported transaction, the filing states that the reporting person beneficially owns 1,033,803 shares of Hyliion common stock in direct ownership form.

Why were the 12,949 Hyliion (HYLN) shares sold in this Form 4 filing?

The explanation of responses notes that the 12,949 shares were sold at the direction of the issuer under an award agreement to cover the reporting person’s tax withholding obligations, and that the issuer has sole discretion to decide on such sales.

Is this Hyliion (HYLN) Form 4 filed for one or multiple reporting persons?

The filing indicates that it is a Form filed by one reporting person, not a joint or group filing.