Inhibrx CEO buys 25,000 shares on Sept. 8

Rhea-AI Filing Summary

Inhibrx Biosciences, Inc. (INBX) reported that Chief Executive Officer and director Mark P. Lappe, through the Lappe Family Trust, purchased a total of 25,000 shares of common stock on September 8, 2026 in multiple open-market transactions at weighted-average prices around $99–$112 per share. The filing also reports additional indirect holdings in a family trust and a Roth IRA.

Insider Trade Summary

Net Buyer: 25,000 shares

Net Buy 8 txns

Insider Lappe Mark

Role Chief Executive Officer

Bought 25,000 shs ($2.65M)

Type	Security	Shares	Price	Value
Purchase	Common Stock F1, F2	5,895	$99.2948	$585K
Purchase	Common Stock F3, F2	6,605	$100.6388	$665K
Purchase	Common Stock F4, F2	1,100	$107.1239	$118K
Purchase	Common Stock F5, F2	500	$108.235	$54K
Purchase	Common Stock F6, F2	1,219	$111.8805	$136K
Purchase	Common Stock F7, F2	9,681	$112.2819	$1.09M
holding	Common Stock F8	--	--	--
holding	Common Stock	--	--	--

Holdings After Transaction: Common Stock — 730,548 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 (8)

1. F1. The shares were purchased in multiple transactions at prices ranging from $98.88 to $99.8316 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 $100.095 to $100.99 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 $106.6225 to $107.57 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 $108.05 to $108.66 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. The shares were purchased in multiple transactions at prices ranging from $111.15 to $112.07 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.
7. F7. The shares were purchased in multiple transactions at prices ranging from $112.15 to $112.44 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.
8. F8. 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

Shares purchased (aggregate): 25,000 shares Purchase tranche 1: 5,895 shares at $99.2948 per share Purchase tranche 2: 6,605 shares at $100.6388 per share +3 more

6 metrics

Shares purchased (aggregate) 25,000 shares Common stock bought indirectly via Lappe Family Trust on September 8, 2026

Purchase tranche 1 5,895 shares at $99.2948 per share Weighted-average price; multiple trades between $98.88 and $99.8316

Purchase tranche 2 6,605 shares at $100.6388 per share Weighted-average price; trades between $100.095 and $100.99

Highest-priced tranche 9,681 shares at $112.2819 per share Weighted-average price; trades between $112.15 and $112.44

Family trust holdings 165,000 shares Common stock held indirectly by a trust for the reporting person’s immediate family

Roth IRA holdings 54,865 shares Common stock held indirectly by The Mark Paul Lappe Roth IRA

Key Terms

weighted-average purchase price, indirectly beneficially own, multiple transactions, immediate family

4 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"

multiple transactions financial

"The shares were purchased in multiple transactions at prices ranging"

immediate family financial

"a trust, for the benefit of the reporting person's immediate family"

FAQ

What did INBX’s CEO report in this Form 4?

The Form 4 reports that CEO and director Mark P. Lappe, through the Lappe Family Trust, purchased 25,000 shares of Inhibrx Biosciences common stock on September 8, 2026 in multiple open-market transactions at various prices.

How many INBX shares did the CEO-associated trust buy and at what prices?

The Lappe Family Trust bought an aggregate of 25,000 shares of INBX on September 8, 2026, in several trades with weighted-average prices of $99.2948, $100.6388, $107.1239, $108.2350, $111.8805, and $112.2819 per share.

Were the INBX insider purchases under a Rule 10b5-1 trading plan?

No. The filing’s Rule 10b5-1 checkbox is not marked as affirmative, and no footnote indicates a trading plan. The transactions are reported as purchases in the open market or private transactions without a stated Rule 10b5-1 plan.

How are the purchased INBX shares held according to the Form 4?

The 25,000 purchased shares are reported as held indirectly by the Lappe Family Trust. A footnote states that Mark P. Lappe is a trustee and may be deemed to indirectly beneficially own the securities owned by that trust.

What other indirect INBX holdings are reported for the CEO?

The Form 4 lists indirect holdings of 165,000 shares of common stock held by a trust for the reporting person’s immediate family and 54,865 shares held by The Mark Paul Lappe Roth IRA.

Did the Form 4 report any INBX share sales or derivative transactions?

No share sales or derivative transactions are reported. The transaction summary shows 6 purchase transactions totaling 25,000 shares bought, with no sales and no derivative exercises disclosed in this filing.

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Available on EDGAR 09/08/2026 - 04:05 PM Accepted by SEC EDGAR 09/08/2026 - 04:04 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)
09/08/2026

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		5,895	A	$99.2948(1)	711,443	I	By the Lappe Family Trust(2)
Common Stock	09/08/2026		P		6,605	A	$100.6388(3)	718,048	I	By the Lappe Family Trust(2)
Common Stock	09/08/2026		P		1,100	A	$107.1239(4)	719,148	I	By the Lappe Family Trust(2)
Common Stock	09/08/2026		P		500	A	$108.235(5)	719,648	I	By the Lappe Family Trust(2)
Common Stock	09/08/2026		P		1,219	A	$111.8805(6)	720,867	I	By the Lappe Family Trust(2)
Common Stock	09/08/2026		P		9,681	A	$112.2819(7)	730,548	I	By the Lappe Family Trust(2)
Common Stock								165,000	I	By Lappe Descendants' Trust(8)
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 $98.88 to $99.8316 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 $100.095 to $100.99 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 $106.6225 to $107.57 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 $108.05 to $108.66 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. The shares were purchased in multiple transactions at prices ranging from $111.15 to $112.07 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.

7. The shares were purchased in multiple transactions at prices ranging from $112.15 to $112.44 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.

8. 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	09/08/2026
	** 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)