Inhibrx director buys 5,000 shares at $113.52

A family trust associated with director Jon Faiz Kayyem bought 5,000 INBX shares around $113.5, increasing reported indirect trust and custodial holdings.

Rhea-AI Filing Summary

Inhibrx Biosciences, Inc. (INBX) director Jon Faiz Kayyem reported that The Jon F. Kayyem and Paige Gates-Kayyem Family Trust purchased 5,000 shares of common stock on September 8, 2026 at a weighted-average price of $113.52 per share in open-market transactions, with prices ranging from $113.30 to $113.55.

After this purchase, that Family Trust held 424,360 shares indirectly attributed to Kayyem, for which he disclaims beneficial ownership except for any indirect pecuniary interest. Additional indirect holdings reported include 250,000 shares in the Jon Faiz Kayyem Revocable Trust, 250,000 shares in the Paige Gates-Kayyem Revocable Trust, and 69,843 shares in custodial accounts for each of two minor children.

Insider Trade Summary

Net Buyer: 5,000 shares

Net Buy 5 txns

Insider Kayyem Jon Faiz

Role Director

Bought 5,000 shs ($568K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F1, F2	5,000	$113.516	$568K
holding	Common Stock F3	--	--	--
holding	Common Stock F4	--	--	--
holding	Common Stock F5	--	--	--
holding	Common Stock F6	--	--	--

Holdings After Transaction: Common Stock — 424,360 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 (6)

1. F1. The shares were purchased in multiple transactions at prices ranging from $113.30 to $113.55 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. 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.
3. F3. These securities are directly owned by the Jon Faiz Kayyem Revocable Trust, of which Jon Faiz Kayyem is the trustee.
4. F4. These securities are directly owned by the Paige-Gates Kayyem Revocable Trust, of which Jon Faiz Kayyem's spouse is the trustee.
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 A. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.
6. F6. 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 Weighted-average purchase price: $113.52 per share Trade price range: $113.30–$113.55 per share +4 more

7 metrics

Shares purchased 5,000 shares Common stock bought on September 8, 2026 by the family trust

Weighted-average purchase price $113.52 per share Open-market purchase of 5,000 INBX shares on September 8, 2026

Trade price range $113.30–$113.55 per share Price range for multiple purchase transactions on September 8, 2026

Family Trust holdings after transaction 424,360 shares Common stock held by The Jon F. Kayyem and Paige Gates-Kayyem Family Trust

Jon Faiz Kayyem Revocable Trust holdings 250,000 shares Indirectly reported INBX common stock holdings

Paige Gates-Kayyem Revocable Trust holdings 250,000 shares Indirectly reported INBX common stock holdings

Each minor child custodial account holdings 69,843 shares Indirect holdings for Child A and Child B, respectively

Key Terms

weighted-average purchase price, indirect pecuniary interest, Revocable Trust, custodial account

4 terms

weighted-average purchase price financial

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

indirect pecuniary interest financial

"except to the extent of any indirect pecuniary interest in his distributive"

Revocable Trust financial

"These securities are directly owned by the Jon Faiz Kayyem Revocable Trust"

A revocable trust is a legal arrangement where the person who creates it keeps control and can change or cancel the trust at any time, while naming who will manage and receive the assets later. Think of it like a flexible folder for your investments and property that can be relabeled or reworked as circumstances change; it matters to investors because it determines how ownership is recorded, how easily assets transfer on incapacity or death, and whether holdings bypass public probate proceedings.

custodial account financial

"These securities are directly owned by a custodial account managed by the"

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.

FAQ

What insider transaction did INBX director Jon Faiz Kayyem report?

He reported that a family trust purchased 5,000 shares of Inhibrx Biosciences common stock on September 8, 2026 in open-market transactions, at a weighted-average price of $113.52 per share, with individual trade prices between $113.30 and $113.55.

At what price were the 5,000 INBX shares purchased?

The 5,000 INBX shares were bought at a weighted-average price of $113.52 per share. The footnote states the trades occurred in multiple transactions at prices ranging from $113.30 to $113.55 per share, all on September 8, 2026.

How many INBX shares does the family trust hold after this transaction?

Following the reported purchase, The Jon F. Kayyem and Paige Gates-Kayyem Family Trust holds 424,360 shares of Inhibrx Biosciences common stock. These shares are reported as indirectly owned, and Kayyem disclaims beneficial ownership except for any indirect pecuniary interest.

What other indirect INBX holdings associated with Jon Faiz Kayyem are disclosed?

The filing lists 250,000 shares held by the Jon Faiz Kayyem Revocable Trust, 250,000 shares held by the Paige Gates-Kayyem Revocable Trust, and 69,843 shares in each of two custodial accounts for minor children, all reported as indirect holdings.

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

No. The filing’s Rule 10b5-1 checkbox is not marked as affirming a trading plan, and the footnotes do not state that the September 8, 2026 purchases were made pursuant to a Rule 10b5-1 or other pre-arranged trading plan.

Does Jon Faiz Kayyem claim full beneficial ownership of the reported INBX shares?

No. For the family trust and the minor children’s custodial accounts, the filing states that he disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

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Available on EDGAR 09/08/2026 - 05:24 PM Accepted by SEC EDGAR 09/08/2026 - 05:23 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)
09/08/2026

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		5,000	A	$113.516(1)	424,360	I	By The Jon F. Kayyem and Paige Gates-Kayyem Family Trust(2)
Common Stock								250,000	I	By Jon Faiz Kayyem Revocable Trust(3)
Common Stock								250,000	I	By Paige Gates-Kayyem Revocable Trust(4)
Common Stock								69,843	I	By Child A(5)
Common Stock								69,843	I	By Child B(6)

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 $113.30 to $113.55 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. 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.

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

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

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 A. The reporting person disclaims beneficial ownership of these securities, except to the extent of any indirect pecuniary interest in his distributive shares therein.

6. 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	09/08/2026
	** 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)