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
X	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* RA CAPITAL MANAGEMENT, L.P. (Last) (First) (Middle) 200 BERKELEY STREET (Street) BOSTON MA 02116 (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) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 04/02/2024
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person
	Rule 10b5-1(c) Transaction Indication Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

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	04/02/2024		C		1,587,912	A	(1)	1,587,912	I	See footnotes(2)(3)
Common Stock	04/02/2024		P		296,875	A	$16	1,884,787	I	See footnotes(2)(3)
Common Stock	04/02/2024		C		280,219	A	(1)	280,219	I	See footnotes(3)(4)
Common Stock	04/02/2024		P		15,625	A	$16	295,844	I	See footnotes(3)(4)

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
Series B Preferred Stock	(1)	04/02/2024		C			17,000,000	(1)	(1)	Common Stock	871,794	$0	0	I	See footnotes(2)(3)
Series B Preferred Stock	(1)	04/02/2024		C			3,000,000	(1)	(1)	Common Stock	153,846	$0	0	I	See footnotes(3)(4)
Series C Preferred Stock	(1)	04/02/2024		C			13,964,285	(1)	(1)	Common Stock	716,118	$0	0	I	See footnotes(2)(3)
Series C Preferred Stock	(1)	04/02/2024		C			2,464,286	(1)	(1)	Common Stock	126,373	$0	0	I	See footnotes(3)(4)

1. Name and Address of Reporting Person* RA CAPITAL MANAGEMENT, L.P. (Last) (First) (Middle) 200 BERKELEY STREET (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* RA Capital Healthcare Fund LP (Last) (First) (Middle) 200 BERKELEY STREET (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* RA Capital Nexus Fund II, L.P. (Last) (First) (Middle) 200 BERKELEY STREET (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Kolchinsky Peter (Last) (First) (Middle) C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Shah Rajeev M. (Last) (First) (Middle) RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

Explanation of Responses:

1. On April 2, 2024, each share of Series B Preferred Stock and Series C Preferred Stock automatically converted into shares of Common Stock on a 19.5-for-1 basis immediately prior to the closing of the Issuer's initial public offering. The shares of Series B Preferred Stock and Series C Preferred Stock had no expiration date.

2. Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

3. RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund and RA Capital Nexus Fund II, L.P. (the "Nexus Fund II"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

4. Held directly by the Nexus Fund II.

	/s/ Peter Kolchinsky, Manager of RA Capital Management, L.P.	04/04/2024
	/s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC the General Partner of RA Capital Healthcare Fund, L.P.	04/04/2024
	/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund II GP, LLC the General Partner of RA Capital Nexus Fund II, L.P.	04/04/2024
	/s/ Peter Kolchinsky, individually	04/04/2024
	/s/ Rajeev Shah, individually	04/04/2024
	** 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).
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