Custom Truck director granted and exercises RSUs

Custom Truck One Source director Mark Ein increased his equity stake through stock-based compensation.

Rhea-AI Filing Summary

Custom Truck One Source director Mark Ein increased his equity stake through stock-based compensation. On March 31, 2026, previously granted restricted stock units representing 26,859 shares vested and were exercised into 26,859 shares of common stock, with no sale reported. On April 1, 2026, he received a new grant of 19,225 restricted stock units, each representing a right to one share of common stock, which will vest on March 31, 2027. Following these transactions, Ein directly holds 5,166,178 shares of common stock.

Insider Trade Summary

26,859 shares exercised/converted

Exercise 3 txns

Insider EIN MARK

Role Director

Type	Security	Shares	Price	Value
Grant/Award	Restricted Stock Unit	19,225	$0.00	$0.00
Exercise	Restricted Stock Unit	26,859	$0.00	$0.00
Exercise	Common Stock	26,859	$0.00	$0.00

Holdings After Transaction: Restricted Stock Unit — 19,225 contracts (Direct); Common Stock — 5,166,178 shares (Direct)

Footnotes (3)

1. F1. Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.
2. F2. The restricted stock units vested in full on March 31, 2026.
3. F3. The restricted stock units will vest on March 31, 2027 and have no expiration date.

Key Figures

New RSU grant: 19,225 units RSUs vested and exercised: 26,859 units Common shares after transactions: 5,166,178 shares +4 more

7 metrics

New RSU grant 19,225 units Restricted stock units granted on April 1, 2026

RSUs vested and exercised 26,859 units Restricted stock units vested and converted on March 31, 2026

Common shares after transactions 5,166,178 shares Direct CTOS common stock held by Mark Ein after March 31, 2026 exercise

Underlying shares for new RSUs 19,225 shares Each new restricted stock unit equals one CTOS common share

Underlying shares for vested RSUs 26,859 shares Previously granted restricted stock units that vested into CTOS common stock

Exercise transactions 1 exercise, 26,859 shares Derivative exercise/conversion transactions summarized in filing

Total acquire-side transactions 3 transactions All transactions classified as acquisitions in transaction summary

Key Terms

Restricted Stock Unit, derivative security, Form 4, vested in full, +1 more

5 terms

Restricted Stock Unit financial

"Each restricted stock unit represents a contingent right to receive one share"

A restricted stock unit is a promise from a company to give an employee shares of stock after certain conditions are met, like staying with the company for a set amount of time. It’s like earning a bonus that turns into company stock once you’ve proven your commitment, making it a way to motivate and reward employees.

derivative security financial

"Exercise or conversion of derivative security"

A derivative security is a financial contract whose value comes from the price or performance of something else, such as a stock, bond, commodity, or market index. For investors it acts like an insurance policy or a wager: it can be used to protect against losses, lock in prices, or amplify gains and losses, so it can change a portfolio’s risk and potential return without owning the underlying asset directly.

Form 4 regulatory

"This Form 4 shows only compensation-related activity"

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.

vested in full financial

"The restricted stock units vested in full on March 31, 2026."

contingent right financial

"represents a contingent right to receive one share of the Issuer's common stock"

FAQ

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

What insider transactions did CTOS director Mark Ein report on this Form 4?

Mark Ein reported three acquire-side transactions: a grant of 19,225 restricted stock units, the vesting and exercise of 26,859 restricted stock units, and receipt of 26,859 common shares with no corresponding sale disclosed.

How many CTOS common shares does Mark Ein hold after these transactions?

After the reported transactions, Mark Ein directly holds 5,166,178 shares of Custom Truck One Source common stock. This total reflects the 26,859 shares received from vested restricted stock units and indicates a sizable continuing ownership position in CTOS.

What restricted stock unit awards did Mark Ein receive from CTOS?

Mark Ein received a grant of 19,225 restricted stock units, each representing a contingent right to one CTOS common share. According to the disclosure, these units will vest in full on March 31, 2027 and have no stated expiration date.

When did Mark Ein’s CTOS restricted stock units vest and convert to shares?

A block of restricted stock units vested in full on March 31, 2026, covering 26,859 underlying CTOS common shares. These units were exercised or converted into an equal number of common shares, with no simultaneous sale reported in this Form 4 filing.

Were there any open-market buys or sells of CTOS shares in this Form 4?

No open-market purchases or sales were reported. The Form 4 shows only compensation-related activity: vesting and conversion of 26,859 restricted stock units into shares and a new grant of 19,225 restricted stock units to director Mark Ein.

What do the CTOS Form 4 footnotes say about Mark Ein’s restricted stock units?

The footnotes state each restricted stock unit equals one CTOS common share. They clarify that one set of units vested in full on March 31, 2026, while another set granted to Mark Ein will vest on March 31, 2027 and has no expiration date.

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

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Accepted by SEC EDGAR 04/02/2026 - 04:30 PM EDT 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^*

EIN MARK

(Last) (First) (Middle)

7701 INDEPENDENCE AVE

(Street)

KANSAS CITY MISSOURI 64125

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Custom Truck One Source, Inc. [ CTOS ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/31/2026

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	03/31/2026		M		26,859	A	$0(1)	5,166,178	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
Restricted Stock Unit	(1)	03/31/2026		M			26,859	(2)	(2)	Common Stock	26,859	$0	0	D
Restricted Stock Unit	(1)	04/01/2026		A		19,225		(3)	(3)	Common Stock	19,225	$0	19,225	D

Explanation of Responses:

1. Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

2. The restricted stock units vested in full on March 31, 2026.

3. The restricted stock units will vest on March 31, 2027 and have no expiration date.

	By: /s/ Paul M. Jolas, Attorney-in-fact	04/02/2026
	** 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)