Boundless Bio CEO awarded 600,000 stock options

Boundless Bio, Inc. reported that its President and CEO, Zachary Hornby, received a grant of a stock option covering 600,000 shares of common stock.

Rhea-AI Filing Summary

Boundless Bio, Inc. reported that its President and CEO, Zachary Hornby, received a grant of a stock option covering 600,000 shares of common stock. The option has an exercise price of $1.26 per share and was granted on January 23, 2026.

The option begins vesting from a commencement date of January 1, 2026, in 48 substantially equal monthly installments. As a result, 1/48th of the option vests on February 1, 2026, with additional monthly vesting thereafter until fully vested, and it is scheduled to expire on January 22, 2036.

Insider Trade Summary

Grant/Award: 600,000 shares

Grant/Award 1 txn

Insider Hornby Zachary

Role President & CEO

Type	Security	Shares	Price	Value
Grant/Award	Stock Option (right to buy)	600,000	$0.00	$0.00

Holdings After Transaction: Stock Option (right to buy) — 600,000 contracts (Direct)

Footnotes (1)

1. F1. The vesting commencement date is January 1, 2026. The stock option vests in 48 substantially equal monthly installments. Accordingly, 1/48th of this stock option vests on February 1, 2026, and monthly thereafter.

FAQ

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

What insider transaction did Boundless Bio (BOLD) disclose in this Form 4?

The filing shows that President & CEO Zachary Hornby received a stock option grant for 600,000 shares of common stock on January 23, 2026.

What is the exercise price of the new stock options granted to the Boundless Bio (BOLD) CEO?

The stock option granted to the CEO has an exercise price of $1.26 per share for the underlying common stock.

How do the Boundless Bio (BOLD) CEO’s new stock options vest?

The option has a vesting commencement date of January 1, 2026 and vests in 48 substantially equal monthly installments, with 1/48th vesting on February 1, 2026 and monthly thereafter.

When do the Boundless Bio (BOLD) CEO’s stock options expire?

The stock option granted to the CEO is scheduled to expire on January 22, 2036, if not exercised or terminated earlier under its terms.

How many stock options does the Boundless Bio (BOLD) CEO hold after this transaction?

Following this grant, the filing reports that the CEO beneficially owns 600,000 derivative securities in the form of stock options, held directly.

Is the Boundless Bio (BOLD) CEO’s option grant reported as directly or indirectly owned?

The Form 4 indicates the 600,000 stock options are held under direct ownership by the reporting person.

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

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Accepted by SEC EDGAR 01/26/2026 - 07:00 AM 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^*

Hornby Zachary

(Last) (First) (Middle)

C/O BOUNDLESS BIO, INC.

10955 ALEXANDRIA WAY, SUITE 100

(Street)

SAN DIEGO CA 92121

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Boundless Bio, Inc. [ BOLD ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
01/23/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

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

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
Stock Option (right to buy)	$1.26	01/23/2026		A		600,000		(1)	01/22/2036	Common Stock	600,000	$0	600,000	D

Explanation of Responses:

1. The vesting commencement date is January 1, 2026. The stock option vests in 48 substantially equal monthly installments. Accordingly, 1/48th of this stock option vests on February 1, 2026, and monthly thereafter.

	/s/ Jessica Oien, Attorney-in- Fact for Zachary Hornby	01/23/2026
	** 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.