Castellum (NYSE: CTM) director sells 55,000 shares in open-market trade

Rhea-AI Filing Summary

Castellum, Inc. director Charles Thomas McMillen sold shares in an open-market transaction. On March 18, 2026, he sold 55,000 shares of Common Stock at an average price of $0.8018 per share. After this sale, he continues to hold 261,015 shares directly, meaning he retained the majority of his stake.

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^*

McMillen Charles Thomas

(Last) (First) (Middle)

1103 SOUTH CAROLINA AVENUE

(Street)

WASHINGTON DISTRICT OF COLUMBIA 20003

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Castellum, Inc. [ CTM ]

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)
03/18/2026

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	03/18/2026		S		55,000	D	$0.8018	261,015	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:

Remarks:

	/s/ C. Thomas McMillen	03/20/2026
	** 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)

FAQ

What insider transaction did Castellum, Inc. (CTM) disclose for Charles Thomas McMillen?

Castellum, Inc. disclosed that director Charles Thomas McMillen completed an open-market sale of common stock. He sold 55,000 shares on March 18, 2026, and this transaction was reported on a Form 4 insider trading filing with the SEC.

How many Castellum (CTM) shares did Charles Thomas McMillen sell and at what price?

Charles Thomas McMillen sold 55,000 shares of Castellum common stock. The reported average sale price was $0.8018 per share, indicating an open-market transaction at a relatively low share price level based on this specific filing data.

How many Castellum, Inc. (CTM) shares does Charles Thomas McMillen hold after this sale?

Following the reported sale, Charles Thomas McMillen directly holds 261,015 shares of Castellum common stock. This shows that, despite the transaction, he maintains a substantial remaining position according to the share balance reported in the Form 4.

Was the Castellum (CTM) insider transaction by Charles Thomas McMillen a buy or a sell?

The transaction was a sell. The Form 4 lists transaction code “S” and describes it as an open-market sale of common stock, confirming that McMillen disposed of shares rather than acquiring additional Castellum stock in this filing.

What type of security did Charles Thomas McMillen trade in the Castellum (CTM) filing?

The filing shows that Charles Thomas McMillen traded Castellum’s Common Stock. It was a non-derivative transaction, meaning it involved actual shares rather than options or other derivative securities, and was executed as an open-market sale.

Does the Castellum (CTM) Form 4 show any option exercises or derivative positions for Charles Thomas McMillen?

No option exercises or derivative positions are listed for this transaction. The Form 4 records only a non-derivative sale of common stock, and the derivative section is empty, indicating no reported options or similar instruments in this particular filing.