Boundless Bio (BOLD): Citadel entities and Ken Griffin report 0.6% ownership

Rhea-AI Filing Summary

Boundless Bio, Inc. received an amended Schedule 13G filing from a group of Citadel-related entities and Kenneth Griffin regarding their holdings of common stock. Based on 22,474,777 Shares outstanding as of June 15, 2026, Citadel Securities LLC may be deemed to beneficially own 65,617 Shares, while each of Citadel Securities Group LP, Citadel Securities GP LLC and Mr. Griffin may be deemed to beneficially own 145,118 Shares, or 0.6% of the outstanding Shares. The filing confirms that the Reporting Persons collectively report ownership of 5 percent or less of this class, with only shared, and no sole, voting or dispositive power over these Shares.

Key Figures

Shares outstanding: 22,474,777 Shares Citadel Securities LLC holdings: 65,617 Shares Griffin reported holdings: 145,118 Shares +2 more

5 metrics

Shares outstanding 22,474,777 Shares Shares outstanding as of June 15, 2026 used for ownership percentages

Citadel Securities LLC holdings 65,617 Shares Beneficially owned by Citadel Securities LLC, representing 0.3% of class

Griffin reported holdings 145,118 Shares Shares Kenneth Griffin may be deemed to beneficially own, 0.6% of class

Citadel Securities Group LP holdings 145,118 Shares Beneficially owned by Citadel Securities Group LP, 0.6% of outstanding Shares

Ownership threshold 5 percent or less Filing states ownership of 5 percent or less of the class

Key Terms

beneficially own, shared voting power, shared dispositive power, Schedule 13G/A, +1 more

5 terms

beneficially own financial

"may be deemed to beneficially own 145,118 Shares"

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.

shared voting power financial

"Shared Voting Power 145,118.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

shared dispositive power financial

"Shared Dispositive Power 145,118.00"

Schedule 13G/A regulatory

"Ownership of 5 Percent or Less of a Class."

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

attorney-in-fact regulatory

"Seth Levy, attorney-in-fact*"

An attorney-in-fact is the person or entity given legal authority through a power of attorney to act on behalf of another for specific tasks, such as signing documents, voting shares, or handling transactions. For investors, this matters because it lets a trusted representative make timely decisions or complete paperwork when the owner cannot, much like handing keys to someone to run errands on your behalf—so checks on scope and limits of that authority are important.

FAQ

What stake in Boundless Bio (BOLD) is reported by Citadel Securities LLC?

Citadel Securities LLC may be deemed to beneficially own 65,617 Shares of Boundless Bio common stock, representing 0.3% of the Shares outstanding based on 22,474,777 Shares outstanding as of June 15, 2026.

How many Boundless Bio (BOLD) shares may Kenneth Griffin be deemed to own?

Kenneth Griffin may be deemed to beneficially own 145,118 Shares of Boundless Bio common stock, which the filing states constitutes 0.6% of the Shares outstanding, using the issuer’s 22,474,777 outstanding Shares figure.

Do the Citadel reporting persons own more than 5% of Boundless Bio (BOLD)?

No. The Schedule 13G/A explicitly states that the Reporting Persons’ holdings constitute 5 percent or less of Boundless Bio’s common stock class, keeping them below the 5% beneficial ownership threshold.

What is the total number of Boundless Bio (BOLD) shares outstanding used in this 13G/A?

The percent-of-class calculations are based on 22,474,777 Shares outstanding as of June 15, 2026, which Boundless Bio reported in a prospectus dated June 23, 2026 and cited by the Reporting Persons.

Do the Citadel entities report sole or shared voting power over Boundless Bio (BOLD) shares?

The filing shows no sole voting power for any Reporting Person. Citadel Securities LLC has 65,617 Shares with shared voting power, and Citadel Securities Group LP, Citadel Securities GP LLC and Kenneth Griffin each report shared voting power over 145,118 Shares.

Who signed the Schedule 13G/A for the Citadel reporting persons in Boundless Bio (BOLD)?

Seth Levy signed as Authorized Signatory for the Citadel entities and as attorney-in-fact for Kenneth Griffin, pursuant to a previously filed power of attorney incorporated by reference.

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

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Available on EDGAR 08/14/2026 - 04:04 PM Accepted by SEC EDGAR 08/14/2026 - 04:01 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Boundless Bio, Inc.

(Name of Issuer)

Common stock, par value $0.0001 per share (the "Shares")

(Title of Class of Securities)

10170A100

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel Advisors LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

0.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.0 %

12

Type of Reporting Person (See Instructions)

IA, HC, OO

Comment for Type of Reporting Person: The percentages reported in this Schedule 13G are based upon 22,474,777 Shares outstanding as of June 15, 2026 (according to the issuer's prospectus as filed with the Securities and Exchange Commission on June 23, 2026).

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel Advisors Holdings LP

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

0.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.0 %

12

Type of Reporting Person (See Instructions)

HC, PN

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel GP LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

0.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.0 %

12

Type of Reporting Person (See Instructions)

HC, OO

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel Securities LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 65,617.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 65,617.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

65,617.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.3 %

12

Type of Reporting Person (See Instructions)

BD, OO

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel Securities Group LP

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 145,118.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 145,118.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

145,118.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.6 %

12

Type of Reporting Person (See Instructions)

HC, PN

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Citadel Securities GP LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 145,118.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 145,118.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

145,118.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.6 %

12

Type of Reporting Person (See Instructions)

HC, OO

SCHEDULE 13G

CUSIP Number(s): 10170A100

1

Names of Reporting Persons

Kenneth Griffin

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 145,118.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 145,118.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

145,118.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.6 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Boundless Bio, Inc.
(b)	Address of issuer's principal executive offices: 11099 North Torrey Pines Road, Suite 150, La Jolla, CA, 92037
Item 2.
(a)	Name of person filing: This Schedule 13G is being jointly filed by Citadel Advisors LLC ("Citadel Advisors"), Citadel Advisors Holdings LP ("CAH"), Citadel GP LLC ("CGP"), Citadel Securities LLC ("Citadel Securities"), Citadel Securities Group LP ("CALC4"), Citadel Securities GP LLC ("CSGP") and Mr. Kenneth Griffin (collectively with Citadel Advisors, CAH, CGP, Citadel Securities, CALC4 and CSGP, the "Reporting Persons") with respect to the Shares of the above-named issuer held of record by Citadel Securities and CRBU Holdings LLC, a Delaware limited liability company ("CRBH"). Such Shares may include other instruments exercisable for or convertible into Shares. CAH is the sole member of Citadel Advisors. CGP is the general partner of CAH. CALC4 is the non-member manager of Citadel Securities and CRBH. CSGP is the general partner of CALC4. Mr. Griffin is the President and Chief Executive Officer of CGP, and owns a controlling interest in CGP and CSGP.
(b)	Address or principal business office or, if none, residence: The address of each of the Reporting Persons is 830 Brickell Plaza, Miami, Florida 33131.
(c)	Citizenship: Each of Citadel Advisors, CGP, Citadel Securities and CSGP is organized as a limited liability company under the laws of the State of Delaware. Each of CALC4 and CAH is organized as a limited partnership under the laws of the State of Delaware. Mr. Griffin is a U.S. citizen.
(d)	Title of class of securities: Common stock, par value $0.0001 per share (the "Shares")
(e)	CUSIP No.: 10170A100
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC may be deemed to beneficially own 0 Shares. 2. Citadel Securities LLC may be deemed to beneficially own 65,617 Shares. 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC may be deemed to beneficially own 145,118 Shares. 4. Mr. Griffin may be deemed to beneficially own 145,118 Shares.
(b)	Percent of class: 1. The number of Shares that each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC may be deemed to beneficially own constitutes 0.0% of the Shares outstanding. 2. The number of Shares that Citadel Securities LLC may be deemed to beneficially own constitutes 0.3% of the Shares outstanding. 3. The number of Shares that each of Citadel Securities Group LP and Citadel Securities GP LLC may be deemed to beneficially own constitutes 0.6% of the Shares outstanding. 4. The number of Shares that Mr. Griffin may be deemed to beneficially own constitutes 0.6% of the Shares outstanding.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 0 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 0 4. Mr. Griffin: 0
	(ii) Shared power to vote or to direct the vote: 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 65,617 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 145,118 4. Mr. Griffin: 145,118
	(iii) Sole power to dispose or to direct the disposition of: 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 0 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 0 4. Mr. Griffin: 0
	(iv) Shared power to dispose or to direct the disposition of: 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 65,617 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 145,118 4. Mr. Griffin: 145,118
Item 5.	Ownership of 5 Percent or Less of a Class.
	Ownership of 5 percent or less of a class
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Citadel Advisors LLC

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Citadel Advisors Holdings LP

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Citadel GP LLC

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Citadel Securities LLC

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Citadel Securities Group LP

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Citadel Securities GP LLC

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, Authorized Signatory
Date:	08/14/2026

Kenneth Griffin

Signature:	/s/ Seth Levy
Name/Title:	Seth Levy, attorney-in-fact*
Date:	08/14/2026

Comments accompanying signature: * Seth Levy is signing on behalf of Kenneth Griffin as attorney-in-fact pursuant to a power of attorney previously filed with the Securities and Exchange Commission, and hereby incorporated by reference herein. The power of attorney was filed as an attachment to a filing by Citadel Advisors LLC on Schedule 13G for Allakos Inc. on October 13, 2023.