Inhibrx Biosciences CEO's trust buys 10,000 shares

Each reported purchase price is a weighted average across multiple trades, and each purchase has its own stated execution-price range.

Rhea-AI Filing Summary

Inhibrx Biosciences, Inc. (INBX) CEO and director Mark P. Lappe reported that the Lappe Family Trust, of which he is a trustee, purchased 10,000 common shares on September 25 and 28, 2026. The four weighted-average prices were $98.8659 (3,324 shares), $99.5988 (2,176), $98.8803 (1,500) and $101.7020 (3,000). No Rule 10b5-1 plan is reported. Separately listed indirect holdings as of September 25, 2026, were 165,000 shares in Lappe Descendants' Trust and 54,865 in the Mark Paul Lappe Roth IRA.

Insider Trade Summary

Net Buyer: 10,000 shares

Net Buy 6 txns

Insider Lappe Mark

Role Chief Executive Officer

Bought 10,000 shs ($999K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F4, F2	1,500	$98.8803	$148K
Purchase	Common Stock F5, F2	3,000	$101.702	$305K
Purchase	Common Stock F1, F2	3,324	$98.8659	$329K
Purchase	Common Stock F3, F2	2,176	$99.5988	$217K
holding	Common Stock F6	--	--	--
holding	Common Stock	--	--	--

Holdings After Transaction: Common Stock — 740,548 shares (Indirect, By the Lappe Family Trust); Common Stock — 165,000 shares (Indirect, By Lappe Descendants' Trust); Common Stock — 54,865 shares (Indirect, The Mark Paul Lappe Roth IRA)

Footnotes (6)

1. F1. The shares were purchased in multiple transactions at prices ranging from $98.27 to $99.26 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 Lappe Family Trust. Mark P. Lappe is a trustee of the Lappe Family Trust and, in such capacity, may be deemed to indirectly beneficially own the securities owned by the Lappe Family Trust.
3. F3. The shares were purchased in multiple transactions at prices ranging from $99.335 to $100.00 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.
4. F4. The shares were purchased in multiple transactions at prices ranging from $98.69 to $99.21 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.
5. F5. The shares were purchased in multiple transactions at prices ranging from $101.44 to $101.80 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.
6. F6. These securities are directly owned by a trust, for the benefit of the reporting person's immediate family. Mark P. Lappe, as an immediate family member of the beneficiaries of the trust, may be deemed to indirectly beneficially own the securities owned by the trust.

Key Figures

September 25 purchase by Lappe Family Trust: 3,324 shares at $98.8659 per share September 25 purchase by Lappe Family Trust: 2,176 shares at $99.5988 per share September 28 purchase by Lappe Family Trust: 1,500 shares at $98.8803 per share +3 more

6 metrics

September 25 purchase by Lappe Family Trust 3,324 shares at $98.8659 per share Weighted-average price for multiple transactions.

September 25 purchase by Lappe Family Trust 2,176 shares at $99.5988 per share Weighted-average price for multiple transactions.

September 28 purchase by Lappe Family Trust 1,500 shares at $98.8803 per share Weighted-average price for multiple transactions.

September 28 purchase by Lappe Family Trust 3,000 shares at $101.7020 per share Weighted-average price for multiple transactions.

Indirect shares held by Lappe Descendants' Trust 165,000 shares As of September 25, 2026.

Indirect shares held in the Mark Paul Lappe Roth IRA 54,865 shares As of September 25, 2026.

Key Terms

weighted-average purchase price, beneficially own, Rule 10b5-1 plan

3 terms

weighted-average purchase price financial

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

beneficially own regulatory

"may be deemed to indirectly beneficially own the securities"

Beneficially own means having the economic rights and risks of a security—such as the right to receive dividends, sell the shares, or profit from price changes—whether or not your name appears on the official share register. Think of it like renting a car: you use it and reap the benefits even if the title lists someone else. Investors care because beneficial ownership determines who truly controls value, must be disclosed under securities rules, and can signal potential influence or trading activity that affects a stock’s price.

Rule 10b5-1 plan regulatory

"No Rule 10b5-1 plan is reported"

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

FAQ

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

How many INBX shares did the Lappe Family Trust buy?

The Lappe Family Trust purchased 10,000 common shares in four reported transactions: 3,324 and 2,176 shares on September 25, 2026, and 1,500 and 3,000 shares on September 28, 2026. Mark P. Lappe, Inhibrx Biosciences' CEO and director, is a trustee of the trust.

What do INBX purchase prices represent?

Each reported price is a weighted-average price for multiple transactions. The underlying price ranges, all inclusive, were $98.27–$99.26 for 3,324 shares, $99.335–$100.00 for 2,176 shares, $98.69–$99.21 for 1,500 shares, and $101.44–$101.80 for 3,000 shares.

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

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Available on EDGAR 09/28/2026 - 05:48 PM Accepted by SEC EDGAR 09/28/2026 - 05:47 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^*

Lappe Mark

(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
X	Officer (give title below)		Other (specify below)
	Chief Executive Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/25/2026

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	09/25/2026		P		3,324	A	$98.8659(1)	733,872	I	By the Lappe Family Trust(2)
Common Stock	09/25/2026		P		2,176	A	$99.5988(3)	736,048	I	By the Lappe Family Trust(2)
Common Stock	09/28/2026		P		1,500	A	$98.8803(4)	737,548	I	By the Lappe Family Trust(2)
Common Stock	09/28/2026		P		3,000	A	$101.702(5)	740,548	I	By the Lappe Family Trust(2)
Common Stock								165,000	I	By Lappe Descendants' Trust(6)
Common Stock								54,865	I	The Mark Paul Lappe Roth IRA

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 $98.27 to $99.26 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 Lappe Family Trust. Mark P. Lappe is a trustee of the Lappe Family Trust and, in such capacity, may be deemed to indirectly beneficially own the securities owned by the Lappe Family Trust.

3. The shares were purchased in multiple transactions at prices ranging from $99.335 to $100.00 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.

4. The shares were purchased in multiple transactions at prices ranging from $98.69 to $99.21 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.

5. The shares were purchased in multiple transactions at prices ranging from $101.44 to $101.80 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.

6. These securities are directly owned by a trust, for the benefit of the reporting person's immediate family. Mark P. Lappe, as an immediate family member of the beneficiaries of the trust, may be deemed to indirectly beneficially own the securities owned by the trust.

Remarks:

	/s/ Kelly D. Deck, as attorney-in-fact for Mark P. Lappe	09/28/2026
	** 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)