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16K Boundless Bio (BOLD) shares sold by ARCH funds post-exercise

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
4

Rhea-AI Filing Summary

Boundless Bio, Inc. received a Form 4 from ARCH-affiliated entities detailing a cashless stock option exercise and same-day sale tied to director Kristina Burow’s compensation. A stock option for 16,000 shares of common stock was exercised at $1.03 per share and the resulting 16,000 shares were sold in an open-market transaction at $2.49 per share. According to the footnotes, the net proceeds from this exercise and sale were remitted to ARCH Venture Fund IX, L.P., ARCH Venture Fund IX Overage, L.P., and ARCH Venture Fund X Overage, L.P., which continue to report substantial indirect holdings of Boundless Bio common stock.

Positive

  • None.

Negative

  • None.
Insider ARCH Venture Fund IX, L.P., ARCH Venture Fund IX Overage, L.P., ARCH Venture Fund X Overage, L.P., ARCH Venture Partners IX, L.P., ARCH Venture Partners IX Overage, L.P., ARCH Venture Partners X Overage, L.P., ARCH Venture Partners IX, LLC, ARCH Venture Partners X, LLC
Role null | null | null | null | null | null | null | null
Sold 16,000 shs ($40K)
Type Security Shares Price Value
Exercise Stock Option (right to buy) 16,000 $0.00 --
Exercise Common Stock 16,000 $1.03 $16K
Sale Common Stock 16,000 $2.49 $40K
holding Common Stock -- -- --
holding Common Stock -- -- --
holding Common Stock -- -- --
Holdings After Transaction: Stock Option (right to buy) — 0 shares (Indirect, See footnote); Common Stock — 16,000 shares (Indirect, See footnote)
Footnotes (1)
  1. Represents a cashless stock option exercise by Kristina Burow. The net proceeds of such exercise were remitted to ARCH Venture Fund IX, L.P. (ARCH IX), ARCH Venture Fund IX Overage, L.P. (ARCH IX Overage), and ARCH Venture Fund X, L.P. (AVF X Overage LP). The stock option was granted to Kristina Burow in connection with her service on the board of directors of the Issuer. 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. 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. 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 IX 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. 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. ARCH Venture Partners X, LLC (AVP X LLC) is the sole general partner of AVP X Overage LP. Keith Crandell, Robert Nelsen, Kristina Burow 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. The stock option vested in substantially equal monthly installments over the 11 months following June 23, 2025. The final unvested portion vested on June 15, 2026, the date of the Issuer's 2026 annual meeting of stockholders.
Shares sold 16,000 shares Common stock sold in open-market transaction
Sale price $2.49 per share Price for 16,000 Boundless Bio shares sold
Option exercise size 16,000 shares Stock option exercised into common stock
Option exercise price $1.03 per share Exercise price of stock option
ARCH IX holding 1,181,766 shares Common stock held indirectly by ARCH Venture Fund IX
ARCH IX Overage holding 828,570 shares Common stock held indirectly by ARCH Venture Fund IX Overage
ARCH X Overage holding 683,759 shares Common stock held indirectly by ARCH Venture Fund X Overage
cashless stock option exercise financial
"Represents a cashless stock option exercise by Kristina Burow."
beneficially own financial
"may be deemed to beneficially own the shares held by ARCH IX"
Beneficially own means having the economic rights and risks of a security—such as the right to receive dividends, sell the shares, or profit from price changes—whether or not your name appears on the official share register. Think of it like renting a car: you use it and reap the benefits even if the title lists someone else. Investors care because beneficial ownership determines who truly controls value, must be disclosed under securities rules, and can signal potential influence or trading activity that affects a stock’s price.
pecuniary interest financial
"each disclaims beneficial ownership except to the extent of any pecuniary interest therein"
indirect financial
"ownership_type: indirect, ownership_code: I"
stock option financial
"The stock option was granted to Kristina Burow in connection with her service"
A stock option is a contract that gives you the right to buy or sell a company's stock at a specific price within a certain time frame. People use them to potentially make money if the stock's price moves favorably or to protect against losses. It's like holding a coupon that can be used to buy or sell stock at a set price later on.
exercise or conversion of derivative security financial
"transaction_code_description: Exercise or conversion of derivative security"
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FAQ

What insider transaction did Boundless Bio (BOLD) report on this Form 4?

The Form 4 reports a cashless stock option exercise for 16,000 Boundless Bio shares at $1.03 per share, followed by an open-market sale of the same 16,000 shares at $2.49 per share, tied to director compensation.

Who is associated with the Boundless Bio (BOLD) Form 4 transactions?

The transactions relate to a stock option granted to director Kristina Burow, with net proceeds remitted to ARCH Venture Fund IX, ARCH Venture Fund IX Overage, and ARCH Venture Fund X Overage, which are the reporting ARCH-affiliated investment funds.

How many Boundless Bio (BOLD) shares were sold by ARCH-affiliated entities?

ARCH-affiliated entities reported the sale of 16,000 shares of Boundless Bio common stock at $2.49 per share. These shares resulted from the same-day exercise of a stock option for 16,000 shares that carried a $1.03 per share exercise price.

What does a cashless stock option exercise mean in the Boundless Bio (BOLD) filing?

A cashless exercise lets the holder use part of the option’s value to cover the exercise cost. Here, a 16,000-share option at $1.03 was exercised and the resulting 16,000 shares were sold at $2.49, with net proceeds delivered to ARCH funds.

Do ARCH funds still hold Boundless Bio (BOLD) shares after this Form 4 event?

Yes. After the reported transactions, ARCH-affiliated entities continue to report indirect ownership of Boundless Bio shares, including 1,181,766 shares of common stock held by ARCH Venture Fund IX, as shown in the holding entries.

What prices were involved in the Boundless Bio (BOLD) option exercise and sale?

The stock option was exercised at an exercise price of $1.03 per share for 16,000 shares. The resulting 16,000 shares of Boundless Bio common stock were then sold in an open-market transaction at $2.49 per share by the ARCH-affiliated entities.
SEC Form 4
FORM 4UNITED 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*
ARCH Venture Fund IX, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(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)
DirectorX10% Owner
Officer (give title below)Other (specify below)
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
07/01/2026
6. Individual or Joint/Group Filing (Check Applicable Line)
Form filed by One Reporting Person
XForm 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)
CodeVAmount(A) or (D)Price
Common Stock07/01/2026M16,000A$1.0316,000ISee footnote(1)
Common Stock07/01/2026S16,000D$2.490ISee footnote(1)
Common Stock683,759ISee footnotes(2)(4)
Common Stock828,570ISee footnotes(3)(4)
Common Stock1,181,766ISee footnotes(5)(6)
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)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock Option (right to buy)$1.0307/01/2026M16,000 (7)06/22/2035Common Stock16,000$00ISee footnote(1)
1. Name and Address of Reporting Person*
ARCH Venture Fund IX, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Fund IX Overage, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Fund X Overage, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Partners IX, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Partners IX Overage, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Partners X Overage, L.P.

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Partners IX, LLC

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
ARCH Venture Partners X, LLC

(Last)(First)(Middle)
8755 W. HIGGINS ROAD, SUITE 1025

(Street)
CHICAGO ILLINOIS 60631

(City)(State)(Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
Explanation of Responses:
1. Represents a cashless stock option exercise by Kristina Burow. The net proceeds of such exercise were remitted to ARCH Venture Fund IX, L.P. (ARCH IX), ARCH Venture Fund IX Overage, L.P. (ARCH IX Overage), and ARCH Venture Fund X, L.P. (AVF X Overage LP). The stock option was granted to Kristina Burow in connection with her service on the board of directors of the Issuer.
2. 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.
3. 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.
4. 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 IX 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.
5. 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.
6. ARCH Venture Partners X, LLC (AVP X LLC) is the sole general partner of AVP X Overage LP. Keith Crandell, Robert Nelsen, Kristina Burow 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.
7. The stock option vested in substantially equal monthly installments over the 11 months following June 23, 2025. The final unvested portion vested on June 15, 2026, the date of the Issuer's 2026 annual meeting of stockholders.
Remarks:
This Form 4 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, Kristina Burow, Steve Gillis and Clint Bybee.
/s/ ARCH Venture Fund X Overage, L.P., By: ARCH Venture Partners X Overage, L.P., its General Partner, By: ARCH Venture Partners X, LLC, its General Partner, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Fund IX, L.P., By: ARCH Venture Partners IX, L.P., its General Partner, By: ARCH Venture Partners IX, LLC, its General Partner, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Fund IX Overage, L.P., By: ARCH Venture Partners IX Overage, L.P., its General Partner, By: ARCH Venture Partners IX, LLC, its General Partner, By: Mark McDonnell attorney in-fact07/06/2026
/s/ ARCH Venture Partners X Overage, L.P. By: ARCH Venture Partners X, LLC, its General Partner, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Partners X, LLC, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Partners IX, L.P., By: ARCH Venture Partners IX, LLC, its General Partner, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Partners IX Overage, L.P., By: ARCH Venture Partners IX, LLC, its General Partner, By: Mark McDonnell, attorney in-fact07/06/2026
/s/ ARCH Venture Partners IX, LLC, By: Mark McDonnell, attorney in-fact07/06/2026
** Signature of Reporting PersonDate
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)