Inhibrx Biosciences family trust buys 5,000 shares

Separate entries show additional shares in two revocable trusts and custodial accounts for Child A and Child B.

Rhea-AI Filing Summary

The Jon F. Kayyem and Paige Gates-Kayyem Family Trust purchased 5,000 common shares of Inhibrx Biosciences, Inc. (INBX) at $100 per share on September 23, 2026, bringing its reported holdings to 434,360 shares. Director Jon Faiz Kayyem disclaims beneficial ownership of the trust shares except to the extent of any indirect pecuniary interest in his distributive shares.

Other listed indirect positions included 250,000 shares in each of the Jon Faiz Kayyem Revocable Trust and Paige Gates-Kayyem Revocable Trust, and 69,843 shares in each custodial account for Child A and Child B. Kayyem disclaims beneficial ownership of the children's account shares except to the extent of any indirect pecuniary interest in his distributive shares.

Insider Trade Summary

Net Buyer: 5,000 shares

Net Buy 5 txns

Insider Kayyem Jon Faiz

Role Director

Bought 5,000 shs ($500K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F1	5,000	$100.00	$500K
holding	Common Stock F2	--	--	--
holding	Common Stock F3	--	--	--
holding	Common Stock F4	--	--	--
holding	Common Stock F5	--	--	--

Holdings After Transaction: Common Stock — 434,360 shares (Indirect, By The Jon F. Kayyem and Paige Gates-Kayyem Family Trust); Common Stock — 250,000 shares (Indirect, By Jon Faiz Kayyem Revocable Trust); Common Stock — 250,000 shares (Indirect, By Paige Gates-Kayyem Revocable Trust); Common Stock — 69,843 shares (Indirect, By Child A); Common Stock — 69,843 shares (Indirect, By Child B)

Footnotes (5)

1. F1. These securities are directly owned by The Jon F. Kayyem and Paige Gates-Kayyem Family Trust. Jon Faiz Kayyem is the trustee of The Jon Faiz Kayyem and Paige N. Gates Family Trust and he disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.
2. F2. These securities are directly owned by the Jon Faiz Kayyem Revocable Trust, of which Jon Faiz Kayyem is the trustee.
3. F3. These securities are directly owned by the Paige-Gates Kayyem Revocable Trust, of which Jon Faiz Kayyem's spouse is the trustee.
4. F4. These securities are directly owned by a custodial account managed by the reporting person for the benefit of the reporting person's minor child, Child A. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.
5. F5. These securities are directly owned by a custodial account managed by the reporting person for the benefit of the reporting person's minor child, Child B. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

Key Figures

Shares purchased: 5,000 shares Purchase price: $100 per share Family trust holdings after purchase: 434,360 shares +4 more

7 metrics

Shares purchased 5,000 shares Family trust purchase on September 23, 2026

Purchase price $100 per share Family trust purchase on September 23, 2026

Family trust holdings after purchase 434,360 shares Reported on September 23, 2026

Jon Faiz Kayyem Revocable Trust holdings 250,000 shares Reported on September 23, 2026

Paige Gates-Kayyem Revocable Trust holdings 250,000 shares Reported on September 23, 2026

Child A custodial account holdings 69,843 shares Reported on September 23, 2026

Child B custodial account holdings 69,843 shares Reported on September 23, 2026

Key Terms

indirect pecuniary interest, beneficial ownership, custodial account, distributive shares

4 terms

indirect pecuniary interest financial

"any indirect pecuniary interest in his distributive shares therein"

beneficial ownership regulatory

"disclaims beneficial ownership of these securities"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

custodial account financial

"directly owned by a custodial account managed by the reporting person"

A custodial account is an investment or bank account opened and managed by an adult (the custodian) for the benefit of someone who cannot legally control assets, typically a minor. Think of it as a wallet held by a trusted guardian until the beneficiary reaches a legal age: it lets you save and invest on someone’s behalf, affects who makes decisions and who pays taxes, and determines when control of the assets transfers to the beneficiary—details investors watch for tax consequences, ownership rules, and timing of control.

distributive shares financial

"his distributive shares therein"

FAQ

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

How many INBX shares did the family trust buy, and at what price?

The Jon F. Kayyem and Paige Gates-Kayyem Family Trust purchased 5,000 INBX common shares at $100 per share on September 23, 2026.

How many INBX shares did the family trust hold after the purchase?

The family trust reported holdings of 434,360 common shares after the purchase.

Was the INBX purchase reported under a Rule 10b5-1 plan?

No Rule 10b5-1 plan is reported for the purchase.

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

Form 4 Insider Transactions: What Each Field Means →

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Available on EDGAR 09/23/2026 - 04:59 PM Accepted by SEC EDGAR 09/23/2026 - 04:59 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^*

Kayyem Jon Faiz

(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)
09/23/2026

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	09/23/2026		P		5,000	A	$100	434,360	I	By The Jon F. Kayyem and Paige Gates-Kayyem Family Trust(1)
Common Stock								250,000	I	By Jon Faiz Kayyem Revocable Trust(2)
Common Stock								250,000	I	By Paige Gates-Kayyem Revocable Trust(3)
Common Stock								69,843	I	By Child A(4)
Common Stock								69,843	I	By Child B(5)

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 securities are directly owned by The Jon F. Kayyem and Paige Gates-Kayyem Family Trust. Jon Faiz Kayyem is the trustee of The Jon Faiz Kayyem and Paige N. Gates Family Trust and he disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

2. These securities are directly owned by the Jon Faiz Kayyem Revocable Trust, of which Jon Faiz Kayyem is the trustee.

3. These securities are directly owned by the Paige-Gates Kayyem Revocable Trust, of which Jon Faiz Kayyem's spouse is the trustee.

4. These securities are directly owned by a custodial account managed by the reporting person for the benefit of the reporting person's minor child, Child A. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

5. These securities are directly owned by a custodial account managed by the reporting person for the benefit of the reporting person's minor child, Child B. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

Remarks:

	/s/ Kelly Deck, as attorney-in-fact to Jon Faiz Kayyem	09/23/2026
	** 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)