Inhibrx director buys 2,500 shares in open market

A director-associated family trust bought 2,500 INBX shares in the open market at a weighted-average price of about $114.65, bringing its reported holdings to 227,064 shares.

Rhea-AI Filing Summary

Inhibrx Biosciences, Inc. (INBX) director Douglas Forsyth reported an open-market purchase of company stock through a family trust. On September 8, 2026, the Forsyth Family Trust bought 2,500 shares of common stock at a weighted-average price of $114.6469 per share.

The shares are held indirectly via the Forsyth Family Trust Dated July 20, 2001, of which Forsyth is a trustee and may be deemed to indirectly beneficially own the securities. Following this transaction, the trust held 227,064 shares of Inhibrx Biosciences common stock. The price reflects multiple trades between $114.36 and $114.689 per share, and no Rule 10b5-1 trading plan is reported.

Insider Trade Summary

Net Buyer: 2,500 shares

Net Buy 1 txn

Insider FORSYTH DOUGLAS

Role Director

Bought 2,500 shs ($287K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F1, F2	2,500	$114.6469	$287K

Holdings After Transaction: Common Stock — 227,064 shares (Indirect, By the Forsyth Family Trust Dated July 20, 2001)

Footnotes (2)

1. F1. The shares were purchased in multiple transactions at prices ranging from $114.36 to $114.689 inclusive. The reported price reflects the weighted-average purchase price. The reporting person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer full information regarding the number of shares and prices at which the transactions were effected.
2. F2. The reporting person is a trustee of the Forsyth Family Trust Dated July 20, 2001 and, in such capacity, may be deemed to indirectly beneficially own the securities owned by the Forsyth Family Trust Dated July 20, 2001.

Key Figures

Shares purchased: 2,500 shares Weighted-average purchase price: $114.6469 per share Price range of purchases: $114.36–$114.689 per share +2 more

5 metrics

Shares purchased 2,500 shares Common stock bought on September 8, 2026 by the Forsyth Family Trust

Weighted-average purchase price $114.6469 per share Average price for the 2,500 INBX shares purchased on September 8, 2026

Price range of purchases $114.36–$114.689 per share Range of individual trade prices for the reported September 8, 2026 purchase

Shares held after transaction 227,064 shares Forsyth Family Trust holdings of Inhibrx Biosciences common stock after the purchase

Number of buy transactions reported 1 transaction Single non-derivative open-market purchase reported in this Form 4

Key Terms

weighted-average purchase price, indirectly beneficially own, open market or private transaction

3 terms

weighted-average purchase price financial

"The reported price reflects the weighted-average purchase price"

indirectly beneficially own financial

"may be deemed to indirectly beneficially own the securities owned"

open market or private transaction financial

"Purchase in open market or private transaction"

FAQ

What insider transaction did INBX director Douglas Forsyth report?

Douglas Forsyth reported that the Forsyth Family Trust purchased 2,500 shares of Inhibrx Biosciences common stock on September 8, 2026 in an open-market transaction at a weighted-average price of $114.6469 per share.

How many INBX shares does the Forsyth Family Trust hold after this transaction?

After the reported purchase, the Forsyth Family Trust held 227,064 shares of Inhibrx Biosciences, Inc. common stock, as reported in the filing.

Was the INBX insider trade made under a Rule 10b5-1 trading plan?

No. The filing indicates the Rule 10b5-1 checkbox is not marked, and there is no footnote stating that the September 8, 2026 purchase of 2,500 shares was made pursuant to a Rule 10b5-1 trading plan.

At what prices were the INBX shares actually bought in this Form 4 transaction?

The 2,500 shares were purchased in multiple transactions at prices ranging from $114.36 to $114.689 per share. The reported $114.6469 figure is the weighted-average purchase price for these trades.

Does Douglas Forsyth hold the INBX shares directly or indirectly?

The reported holdings are indirect. The shares are owned by the Forsyth Family Trust Dated July 20, 2001, where Douglas Forsyth serves as trustee and may be deemed to indirectly beneficially own the trust’s Inhibrx Biosciences shares.

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Available on EDGAR 09/08/2026 - 04:26 PM Accepted by SEC EDGAR 09/08/2026 - 04:26 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^*

FORSYTH DOUGLAS

(Last) (First) (Middle)

C/O INHIBRX BIOSCIENCES, INC.

11025 NORTH TORREY PINES ROAD, SUITE 140

(Street)

LA JOLLA CALIFORNIA 92037

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Inhibrx Biosciences, Inc. [ INBX ]

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)
09/08/2026

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	09/08/2026		P		2,500	A	$114.6469(1)	227,064	I	By the Forsyth Family Trust Dated July 20, 2001(2)

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. The shares were purchased in multiple transactions at prices ranging from $114.36 to $114.689 inclusive. The reported price reflects the weighted-average purchase price. The reporting person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer full information regarding the number of shares and prices at which the transactions were effected.

2. The reporting person is a trustee of the Forsyth Family Trust Dated July 20, 2001 and, in such capacity, may be deemed to indirectly beneficially own the securities owned by the Forsyth Family Trust Dated July 20, 2001.

Remarks:

	/s/ Kelly D. Deck, as attorney-in-fact for Douglas G. Forsyth	09/08/2026
	** 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)