Sec Form 3 Filing - CRANDELL KEITH @ Boundless Bio, Inc. - 2024-03-27

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person CRANDELL KEITH 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) (Last) (First) (Middle) 8755 WEST HIGGINS ROAD, SUITE 1025 3. Date of Earliest Transaction (MM/DD/YY) 03/27/2024 (Street) CHICAGO, IL60631 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 27,349 I See footnotes ( 1 ) ( 3 ) Common Stock 41,025 I See footnotes ( 2 ) ( 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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 A Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 424,908 I See footnotes ( 1 ) ( 3 ) Series A Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 586,080 I See footnotes ( 2 ) ( 3 ) Series A Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 454,212 I See footnotes ( 4 ) ( 5 ) Series B Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 227,920 I See footnotes ( 4 ) ( 5 ) Series C Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 164,835 I See footnotes ( 1 ) ( 3 ) Series C Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 201,465 I See footnotes ( 2 ) ( 3 ) Series C Convertible Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 366,301 I See footnotes ( 4 ) ( 5 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other CRANDELL KEITH 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X BYBEE CLINTON 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X NELSEN ROBERT 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X GILLIS STEVEN 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X Signatures /s/ Keith Crandell, By: Mark McDonnell, attorney in-fact 03/27/2024 Signature of Reporting Person Date /s/ Clinton Bybee, By: Mark McDonnell, attorney in-fact 03/27/2024 Signature of Reporting Person Date /s/ Robert Nelsen, By: Mark McDonnell, attorney in-fact 03/27/2024 Signature of Reporting Person Date /s/ Steven Gillis, By: Mark McDonnell, attorney in-fact 03/27/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents shares held directly by ARCH Venture Fund IX, L.P. (ARCH IX). ARCH Venture Partners IX, L.P. (AVP IX LP) is the sole general partner of ARCH IX. ( 2 )Represents shares held directly by ARCH Venture Fund IX Overage, L.P. (ARCH IX Overage). ARCH Venture Partners IX Overage, L.P. (AVP IX Overage LP) is the sole general partner of ARCH IX Overage. ( 3 )ARCH Venture Partners IX, LLC (AVP IX LLC) is the sole general partner of each of AVP IX LP and AVP IX Overage LP. Keith Crandell, Robert Nelsen and Clinton Bybee are managing directors of AVP I X LLC (the AVP IX MDs). AVP IX LP and AVP IX Overage LP may be deemed to beneficially own the shares held by ARCH IX and ARCH IX Overage, respectively, AVP IX LLC may be deemed to beneficially own the shares held by ARCH IX and ARCH IX Overage, and each of the AVP IX MDs may be deemed to share the power to direct the disposition and vote of the shares held by ARCH IX and ARCH IX Overage. AVP IX LP, AVP IX Overage LP, AVP IX LLC, and the AVP IX MDs each disclaim beneficial ownership except to to the extent of any pecuniary interest therein, if any. ( 4 )Represents shares held directly by ARCH Venture Fund X Overage, L.P. (ARCH X Overage). ARCH Venture Partners X Overage, L.P. (AVP X Overage LP) is the sole general partner of ARCH X Overage. ( 5 )ARCH Venture Partners X, LLC (AVP X LLC) is the sole general partner of AVP X Overage LP. Keith Crandell, Robert Nelsen and Steven Gillis are members of the investment committee of AVP X LLC (the AVP X Committee Members). AVP X Overage LP may be deemed to beneficially own the shares held by ARCH X Overage, AVP X LLC may be deemed to beneficially own the shares held by ARCH X Overage, and each of the AVP X Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH X Overage. AVP X Overage LP, AVP X LLC, and the AVP X Committee Members each disclaim beneficial ownership except to the extent of any pecuniary interest therein., if any. ( 6 )Each share of the Issuer's preferred stock is convertible into shares of the Issuer's common stock at the holder's election and has no expiration date. The preferred stock will automatically convert into common stock upon the closing of the Issuer's initial public offering.

Remarks: This Form 3 is one of two reports relating to the same transaction being filed jointly by ARCH IX, AVP IX LP, ARCH IX Overage, AVP IX Overage LP, AVP IX LLC, ARCH X Overage, AVP X Overage LP, AVP X LLC, Robert Nelsen, Keith Crandell, Steve Gillis and Clint Bybee (collectively, the "Reporting Persons"). Kristina Burow is filing her own Form 3 separately.

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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