Boundless Bio owners buy 149,474 common shares

The reported purchases were indirect, and Kevin Tang’s footnoted pecuniary interest relates to shares beneficially held by four Tang Capital entities.

Rhea-AI Filing Summary

Boundless Bio, Inc. ten-percent owners Kevin Tang and Tang Capital Management LLC reported four indirect purchases totaling 149,474 common shares from October 16 through October 20, 2026. The entries were 118,185 shares on October 16 at a weighted-average $2.34 per share; 12,790 shares on October 19 at $2.34; 18,279 shares that day at $2.33; and 220 shares on October 20 at $2.37. Footnotes give the respective transaction price ranges as $2.31–$2.35, $2.31–$2.35, $2.32–$2.35, and $2.33–$2.40. A footnote identifies Kevin Tang’s pecuniary interest in shares beneficially held by Tang Capital Partners, LP; Tang Capital Partners International, LP; Tang Capital Partners III, Inc.; and Tang Capital Partners IV, Inc. The reporting persons stated they delivered $1,723.10 to Boundless Bio. No Rule 10b5-1 plan is reported.

Insider Trade Summary

Net Buyer: 149,474 shares

Net Buy 4 txns

Insider TANG KEVIN, TANG CAPITAL MANAGEMENT LLC

Role 10% Owner | 10% Owner

Bought 149,474 shs ($350K)

Type	Security	Shares	Price	Value
Purchase	Common Stock F6, F3	220	$2.37	$521.40
Purchase	Common Stock F1, F4, F3	12,790	$2.34	$30K
Purchase	Common Stock F1, F5, F3	18,279	$2.33	$43K
Purchase	Common Stock F1, F2, F3	118,185	$2.34	$277K

Holdings After Transaction: Common Stock — 2,990,109 shares (Indirect, See Footnote)

Footnotes (6)

1. F1. The Reporting Persons have delivered to the Issuer the full amount of the disgorgeable profit arising the purchases reported herein, in the amount of $1,723.10.
2. F2. The prices reported are weighted-average prices. These shares were purchased in multiple transactions at prices ranging from $2.31 to $2.35. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the SEC staff, upon request, all information regarding the number of shares purchased at each price within the range set forth in Footnotes 2 and 4 through 6.
3. F3. Tang Capital Partners, LP ("TCP") beneficially owns 688,494 shares, Tang Capital Partners International, LP ("TCPI") beneficially owns 937,213 shares, Tang Capital Partners III, Inc. ("TCP III") beneficially owns 688,487 shares, and Tang Capital Partners IV, Inc. ("TCP IV") beneficially owns 675,915 shares. Kevin Tang is the sole manager of Tang Capital Management, LLC, which is the general partner of TCP and TCPI. Kevin Tang is the sole director and Chief Executive Officer of TCP III and TCP IV, which are indirectly wholly owned by TCP. Mr. Tang has a pecuniary interest in the shares beneficially held by TCP, TCPI, TCP III and TCP IV.
4. F4. These shares were purchased in multiple transactions at prices ranging from $2.31 to $2.35.
5. F5. These shares were purchased in multiple transactions at prices ranging from $2.32 to $2.35.
6. F6. These shares were purchased in multiple transactions at prices ranging from $2.33 to $2.40.

Key Figures

Common shares purchased: 149,474 shares October 16 purchase: 118,185 shares at a weighted-average $2.34 per share October 19 purchase: 12,790 shares at $2.34 per share +3 more

6 metrics

Common shares purchased 149,474 shares Four indirect purchase entries

October 16 purchase 118,185 shares at a weighted-average $2.34 per share October 16, 2026

October 19 purchase 12,790 shares at $2.34 per share October 19, 2026

October 19 purchase 18,279 shares at $2.33 per share October 19, 2026

October 20 purchase 220 shares at $2.37 per share October 20, 2026

Amount delivered to issuer $1,723.10 Stated by the reporting persons

Key Terms

weighted-average prices, pecuniary interest, beneficially owns

3 terms

weighted-average prices financial

"The prices reported are weighted-average prices."

pecuniary interest financial

"Mr. Tang has a pecuniary interest in the shares"

beneficially owns financial

"Tang Capital Partners, LP ("TCP") beneficially owns 688,494 shares"

Beneficially owns means a person or entity enjoys the economic benefits and control of a security even if the legal title or registration is held in another name. Think of it like having the keys and profits from a car that is registered to a friend: you use it, benefit from it, and make decisions about it even though the official paperwork lists someone else. For investors, this matters because it reveals who truly controls shares, affects voting power, potential conflicts of interest, and regulatory disclosure obligations.

FAQ

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

How many BOLD shares did Kevin Tang and Tang Capital Management LLC purchase?

The reporting persons reported four indirect purchases totaling 149,474 Boundless Bio common shares. The entries were 118,185 shares on October 16, 2026, at a weighted-average $2.34 per share; 12,790 shares on October 19 at $2.34; 18,279 shares that day at $2.33; and 220 shares on October 20 at $2.37.

How much did the BOLD reporting persons deliver to Boundless Bio?

The reporting persons stated that they delivered $1,723.10 to Boundless Bio.

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

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Available on EDGAR 10/20/2026 - 05:49 PM EDT Accepted by SEC EDGAR 10/20/2026 - 05:49 PM EDT 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^*

TANG KEVIN

(Last) (First) (Middle)

4747 EXECUTIVE DRIVE

SUITE 210

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

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

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
10/16/2026

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

	Form filed by One Reporting Person
X	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	10/16/2026		P(1)		118,185	A	$2.34(2)	2,958,820	I	See Footnote(3)
Common Stock	10/19/2026		P(1)		12,790	A	$2.34(4)	2,971,610	I	See Footnote(3)
Common Stock	10/19/2026		P(1)		18,279	A	$2.33(5)	2,989,889	I	See Footnote(3)
Common Stock	10/20/2026		P		220	A	$2.37(6)	2,990,109	I	See Footnote(3)

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

1. Name and Address of Reporting Person^*

TANG KEVIN

(Last) (First) (Middle)

4747 EXECUTIVE DRIVE

SUITE 210

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

1. Name and Address of Reporting Person^*

TANG CAPITAL MANAGEMENT LLC

(Last) (First) (Middle)

4747 EXECUTIVE DRIVE

SUITE 210

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

Explanation of Responses:

1. The Reporting Persons have delivered to the Issuer the full amount of the disgorgeable profit arising the purchases reported herein, in the amount of $1,723.10.

2. The prices reported are weighted-average prices. These shares were purchased in multiple transactions at prices ranging from $2.31 to $2.35. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the SEC staff, upon request, all information regarding the number of shares purchased at each price within the range set forth in Footnotes 2 and 4 through 6.

3. Tang Capital Partners, LP ("TCP") beneficially owns 688,494 shares, Tang Capital Partners International, LP ("TCPI") beneficially owns 937,213 shares, Tang Capital Partners III, Inc. ("TCP III") beneficially owns 688,487 shares, and Tang Capital Partners IV, Inc. ("TCP IV") beneficially owns 675,915 shares. Kevin Tang is the sole manager of Tang Capital Management, LLC, which is the general partner of TCP and TCPI. Kevin Tang is the sole director and Chief Executive Officer of TCP III and TCP IV, which are indirectly wholly owned by TCP. Mr. Tang has a pecuniary interest in the shares beneficially held by TCP, TCPI, TCP III and TCP IV.

4. These shares were purchased in multiple transactions at prices ranging from $2.31 to $2.35.

5. These shares were purchased in multiple transactions at prices ranging from $2.32 to $2.35.

6. These shares were purchased in multiple transactions at prices ranging from $2.33 to $2.40.

	Kevin Tang	10/20/2026
	Kevin Tang, Manager	10/20/2026
	** 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)