Hyliion (NYSE: HYLN) CTO holds 1,096,606 shares after tax sale

Rhea-AI Filing Summary

Hyliion Holdings Corp. (HYLN) reported that Chief Technology Officer Joshua T. Mook disposed of 10,700 shares of common stock on 2026-08-21 at $3.33 per share. According to the award agreement, these shares were sold at the issuer’s direction to cover Mr. Mook’s tax withholding obligations, leaving him with 1,096,606 shares of common stock held directly.

Insider Trade Summary

Net Seller: 10,700 shares

Net Sell 1 txn

Insider MOOK JOSHUA T.

Role Chief Technology Officer

Type	Security	Shares	Price	Value
Other	Common Stock F1	10,700	$3.33	$36K

Holdings After Transaction: Common Stock — 1,096,606 shares (Direct)

Footnotes (1)

1. F1. 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.

Key Figures

Common stock disposed: 10,700 shares Transaction price per share: $3.33 per share Shares owned after transaction: 1,096,606 shares +1 more

4 metrics

Common stock disposed 10,700 shares Shares involved in the 2026-08-21 Form 4 transaction coded J

Transaction price per share $3.33 per share Price for the 10,700 Hyliion common shares in the reported transaction

Shares owned after transaction 1,096,606 shares Directly held Hyliion common shares by Joshua T. Mook after the transaction

Restructuring shares 10,700 shares TransactionSummary restructuringShares associated with code J event

Key Terms

Other acquisition or disposition, award agreement, tax withholding obligations

3 terms

Other acquisition or disposition regulatory

"transaction coded as an “Other acquisition or disposition” (code J)"

award agreement financial

"sold at the direction of the issuer under the terms of the issuer's award agreement"

An award agreement is a legal contract that spells out the terms of a pay or equity grant—such as stock options, restricted shares, or cash bonuses—given to an employee, director or consultant. It describes what is being granted, any conditions for keeping it (for example, earning it over time or meeting performance targets), and what happens if the person leaves or breaks rules. Investors care because these agreements affect company costs, potential share dilution and how executives are motivated and rewarded.

tax withholding obligations financial

"sell shares to cover the reporting person's tax withholding obligations"

FAQ

What insider transaction did HYLN disclose for Joshua T. Mook?

Hyliion Holdings Corp. disclosed that Chief Technology Officer Joshua T. Mook disposed of 10,700 shares of common stock on 2026-08-21 in a transaction coded as an “Other acquisition or disposition” (code J).

At what price were Joshua T. Mook’s HYLN shares transacted?

The 10,700 Hyliion common shares associated with Joshua T. Mook’s transaction were priced at $3.33 per share, as reported in the Form 4 data for the 2026-08-21 transaction.

How many HYLN shares does Joshua T. Mook hold after this transaction?

Following the reported transaction, Chief Technology Officer Joshua T. Mook holds 1,096,606 shares of Hyliion common stock directly, according to the Form 4 disclosure’s post-transaction holdings figure.

Why were Joshua T. Mook’s HYLN shares sold in this Form 4 event?

The Form 4 footnote states that the shares were sold at the direction of the issuer under an award agreement, in which the issuer may sell shares to cover the reporting person’s tax withholding obligations at its sole discretion.

Was Joshua T. Mook’s HYLN transaction under a Rule 10b5-1 plan?

The Form 4 indicates the Rule 10b5-1 checkbox is not affirmed (false), and no footnote describes a Rule 10b5-1 trading plan in connection with this 10,700-share transaction.

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

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Form 4 Insider Transactions: What Each Field Means →

Available on EDGAR 08/21/2026 - 04:51 PM Accepted by SEC EDGAR 08/21/2026 - 04:50 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).

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 TEXAS 78613

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/21/2026

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	08/21/2026		J(1)		10,700	D	$3.33	1,096,606	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	08/21/2026
	** 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)