Hyliion CTO reports tax-related share sales

Rhea-AI Filing Summary

Hyliion Holdings Corp.’s Chief Technology Officer, Joshua T. Mook, reported two small Form 4 transactions in common stock coded as “other acquisition or disposition.” On May 19 and May 20, a total of 6,803 shares were sold at prices of $4.06 and $3.92 per share. A footnote explains these shares were sold at the direction of the issuer under an award agreement to cover Mr. Mook’s tax withholding obligations, meaning they were mechanistic, compensation-related sales rather than discretionary trading. After these transactions, Mr. Mook directly holds 1,107,306 common shares, so the tax-related sales represent a small portion of his overall stake.

Insider Trade Summary

Other: 6,803 shares

Other 2 txns

Insider MOOK JOSHUA T.

Role Chief Technology Officer

Type	Security	Shares	Price	Value
Other	Common Stock	2,003	$3.92	$8K
Other	Common Stock	4,800	$4.06	$19K

Holdings After Transaction: Common Stock — 1,107,306 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

Shares sold May 19: 4,800 shares at $4.06 Shares sold May 20: 2,003 shares at $3.92 Total shares affected: 6,803 shares +1 more

4 metrics

Shares sold May 19 4,800 shares at $4.06 Common stock, transaction code J on May 19

Shares sold May 20 2,003 shares at $3.92 Common stock, transaction code J on May 20

Total shares affected 6,803 shares RestructuringShares across both J-code transactions

Shares held after transactions 1,107,306 shares Direct common stock ownership following May 20 transaction

Key Terms

Form 4, Other acquisition or disposition, award agreement, tax withholding obligations

4 terms

Form 4 regulatory

"Joshua T. Mook reported two small Form 4 transactions in common stock"

Form 4 is a official document that company insiders, such as executives or major shareholders, file with regulators whenever they buy or sell company shares. It provides transparency about how those with inside knowledge are trading, helping investors see if insiders are confident in the company's prospects or may be selling for personal reasons. This information can influence investor decisions by revealing insiders' perspectives on the company's value.

Other acquisition or disposition regulatory

"coded as “other acquisition or disposition.”"

award agreement financial

"under the terms of the issuer's award agreement with the reporting person"

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

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

FAQ

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

What insider transactions did Hyliion (HYLN) report for Joshua T. Mook?

Hyliion’s Chief Technology Officer Joshua T. Mook reported two small Form 4 transactions in common stock. A total of 6,803 shares were sold over May 19–20 under award agreement terms to handle tax withholding obligations rather than discretionary trading.

How many Hyliion (HYLN) shares were involved in Joshua T. Mook’s latest Form 4?

The filing shows 6,803 Hyliion common shares affected across two transactions. These comprised 4,800 shares on May 19 and 2,003 shares on May 20, all sold under an issuer-directed process to cover tax withholding obligations linked to equity compensation.

At what prices were Joshua T. Mook’s Hyliion (HYLN) shares sold?

Shares were sold at two prices: $4.06 per share on May 19 and $3.92 per share on May 20. These sales were executed at the issuer’s direction under an award agreement to satisfy Mr. Mook’s tax withholding obligations from compensation-related equity.

Why were Joshua T. Mook’s Hyliion (HYLN) shares sold according to the Form 4?

The Form 4 footnote states the shares were sold at the issuer’s direction under an award agreement. The sole purpose was covering Joshua T. Mook’s tax withholding obligations, making these routine compensation-related sales rather than open-market trades initiated by the executive.

How many Hyliion (HYLN) shares does Joshua T. Mook hold after these transactions?

Following the reported transactions, Joshua T. Mook directly holds 1,107,306 Hyliion common shares. This indicates the 6,803 shares sold for tax withholding represent a relatively small portion of his total reported direct ownership in the company’s stock.

What does transaction code “J” mean in Joshua T. Mook’s Hyliion (HYLN) Form 4?

Transaction code “J” indicates another type of acquisition or disposition not classified as a standard buy, sell, or option exercise. Here, the Form 4 notes the J-code transactions reflect issuer-directed share sales to cover Joshua T. Mook’s tax withholding obligations under an award agreement.

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

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Accepted by SEC EDGAR 05/21/2026 - 04:21 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)
05/19/2026

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	05/19/2026		J(1)		4,800	D	$4.06	1,109,309	D
Common Stock	05/20/2026		J(1)		2,003	D	$3.92	1,107,306	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	05/21/2026
	** 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)