Magnetar group discloses 2,000,000 Keystone (KEYY) shares, a 6.96% ownership stake

Rhea-AI Filing Summary

Magnetar Financial LLC and related entities report a significant ownership position in Keystone Acquisition Corp. As of June 30, 2026, Magnetar Financial, Magnetar Capital Partners LP, Supernova Management LLC, and David J. Snyderman are each deemed to beneficially own 2,000,000 Class A ordinary shares of Keystone Acquisition Corp, representing approximately 6.96% of the company’s outstanding shares.

The 2,000,000 shares are held across several Magnetar-managed funds, and the reporting persons have shared voting and dispositive power over all of these shares, with no sole voting or dispositive power. The ownership percentage is based on 28,750,000 shares outstanding, as referenced from a Form 8-K filed by the issuer.

Key Figures

Beneficial ownership: 2,000,000 shares Ownership percentage: 6.96% Shares outstanding: 28,750,000 shares +5 more

8 metrics

Beneficial ownership 2,000,000 shares Class A ordinary shares beneficially owned as of June 30, 2026

Ownership percentage 6.96% Percentage of Keystone Acquisition Corp Class A shares outstanding

Shares outstanding 28,750,000 shares Total Class A shares outstanding referenced from Form 8-K

Par value per share $0.0001 Par value of Keystone Acquisition Corp Class A ordinary shares

Shared voting power 2,000,000 shares Shares over which reporting persons have shared voting power

Shared dispositive power 2,000,000 shares Shares over which reporting persons have shared dispositive power

Constellation Master Fund allocation 480,000 shares Portion of the 2,000,000 shares held for Constellation Master Fund

Structured Credit Fund allocation 420,000 shares Portion of the 2,000,000 shares held for Structured Credit Fund

Key Terms

beneficial owner, shared voting power, dispositive power, investment adviser, +2 more

6 terms

beneficial owner financial

"each of the Reporting Persons were deemed to be the beneficial owner constituting approximately 6.96%"

A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.

shared voting power financial

"Shared Voting Power 2,000,000.00"

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.

dispositive power financial

"Shared Dispositive Power 2,000,000.00"

Dispositive power is the authority to decide the final outcome of an asset, legal claim, contract, or corporate action — in effect the power to dispose of or resolve something. For investors it matters because whoever holds that authority can determine who gets paid, who controls an asset or vote, and how risks and returns are allocated; think of it like holding the key that lets you lock in the winner or loser in a deal.

investment adviser financial

"Magnetar Financial serves as the investment adviser to the Magnetar Funds"

An investment adviser is a person or firm that professionally manages money and gives recommendations about buying, selling, or holding investments. Like a financial coach or guide, they have a legal duty to act in a client's best financial interest, so their advice, fees and potential conflicts can directly affect returns and risk — making their role important for investors who want informed, accountable help with portfolios.

attorney-in-fact regulatory

"Title: Attorney-in-fact for David J. Snyderman, Administrative Manager"

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.

Joint Filing Agreement regulatory

"Exhibit Information 99.1 Joint Filing Agreement, dated as of August 13, 2026"

FAQ

What percentage of Keystone Acquisition Corp (KEYY) does Magnetar beneficially own?

Magnetar and related reporting persons beneficially own 6.96% of Keystone Acquisition Corp’s Class A shares. This percentage is based on 2,000,000 shares held versus 28,750,000 shares outstanding as referenced by the issuer.

How many Keystone Acquisition Corp (KEYY) shares are reported by Magnetar?

The reporting persons disclose beneficial ownership of 2,000,000 Class A shares of Keystone Acquisition Corp. These shares are allocated among multiple Magnetar-managed funds, with the group holding shared voting and dispositive power over all of them.

Which entities are the reporting persons in this Keystone (KEYY) Schedule 13G?

The filing is made on behalf of Magnetar Financial LLC, Magnetar Capital Partners LP, Supernova Management LLC, and David J. Snyderman. Together they are deemed beneficial owners of the reported 2,000,000 shares of Keystone Acquisition Corp.

How is Magnetar’s 2,000,000-share Keystone (KEYY) position distributed among its funds?

The 2,000,000 shares include 480,000 for Constellation Master Fund, 340,000 each for Lake Credit, Xing He and Alpha Star, 420,000 for Structured Credit, 20,000 for Capital Master Fund, and 60,000 for Waterfront Series A Fund.

Does Magnetar have sole or shared voting power over its Keystone (KEYY) shares?

The reporting persons have shared voting power over 2,000,000 shares and no sole voting power. They also have shared dispositive power over the same 2,000,000 shares, with no sole dispositive authority.

What is the par value and CUSIP of Keystone Acquisition Corp (KEYY) Class A shares?

Keystone Acquisition Corp’s Class A ordinary shares have a par value of $0.0001 per share and trade under CUSIP G52539114. These details frame the security class reported in the beneficial ownership disclosure.

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

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Available on EDGAR 08/13/2026 - 06:18 AM Accepted by SEC EDGAR 08/13/2026 - 06:17 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

KEYSTONE ACQUISITION CORP

(Name of Issuer)

Class A ordinary shares, par value $0.0001

(Title of Class of Securities)

G52539114

(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): G52539114

1

Names of Reporting Persons

MAGNETAR FINANCIAL 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 2,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,000,000.00

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)

6.96 %

12

Type of Reporting Person (See Instructions)

IA, OO

SCHEDULE 13G

CUSIP Number(s): G52539114

1

Names of Reporting Persons

MAGNETAR CAPITAL PARTNERS 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 2,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,000,000.00

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)

6.96 %

12

Type of Reporting Person (See Instructions)

HC, PN

SCHEDULE 13G

CUSIP Number(s): G52539114

1

Names of Reporting Persons

SUPERNOVA MANAGEMENT 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 2,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,000,000.00

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)

6.96 %

12

Type of Reporting Person (See Instructions)

HC, OO

SCHEDULE 13G

CUSIP Number(s): G52539114

1

Names of Reporting Persons

DAVID J. SNYDERMAN

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 2,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,000,000.00

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)

6.96 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: KEYSTONE ACQUISITION CORP
(b)	Address of issuer's principal executive offices: 142 West 57th Street 11th Floor, NEW YORK, NY 10019
Item 2.
(a)	Name of person filing: This statement is filed on behalf of each of the following person (collectively, the "Reporting Persons"): i) Magnetar Financial LLC ("Magnetar Financial"); ii) Magnetar Capital Partners LP ("Magnetar Capital Partners"); iii) Supernova Management LLC ("Supernova Management"); and iv) David J. Snyderman ("Mr. Snyderman"). This statement relates to the Shares (as defined herein) held for Magnetar Constellation Master Fund, Ltd ("Constellation Master Fund"), Magnetar Xing He Master Fund Ltd ("Xing He Master Fund"), and Magnetar Capital Master Fund Ltd ("Capital Master Fund"), all Cayman Islands exempted companies; Magnetar Structured Credit Fund, LP ("Structured Credit Fund"), a Delaware limited partnership; Magnetar Alpha Star Fund LLC ("Alpha Star Fund"), Magnetar Lake Credit Fund LLC ("Lake Credit Fund"), and Magnetar Waterfront Series A LLC ("Waterfront Series A Fund"), all Delaware limited liability companies; collectively (the "Magnetar Funds"). Magnetar Financial serves as the investment adviser to the Magnetar Funds, and as such, Magnetar Financial exercises voting and investment power over the Shares held for the Magnetar Funds' accounts. Magnetar Capital Partners serves as the sole member and parent holding company of Magnetar Financial. Supernova Management is the general partner of Magnetar Capital Partners. The administrative manager of Supernova Management is Mr. Snyderman.
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of Magnetar Financial, Magnetar Capital Partners, Supernova Management, and Mr. Snyderman is 1603 Orrington Avenue, 13th Floor, Evanston, Illinois 60201.
(c)	Citizenship: Place of Organization. i) Magnetar Financial is a Delaware limited liability company; ii) Magnetar Capital Partners is a Delaware limited partnership; iii) Supernova Management is a Delaware limited liability company; and iv) Mr. Snyderman is a citizen of the United States of America.
(d)	Title of class of securities: Class A ordinary shares, par value $0.0001
(e)	CUSIP Number(s): G52539114
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: As of June 30, 2026, each of Magnetar Financial, Magnetar Capital Partners, Supernova Management and Mr. Snyderman held 2,000,000 Shares. The amount consists of (A) 480,000 Shares held for the account of Constellation Master Fund; (B) 340,000 Shares held for the account of Lake Credit Fund; (C) 420,000 Shares held for the account of Structured Credit Fund; (D) 340,000 Shares held for the account of Xing He Master Fund; (E) 340,000 Shares held for the account of Alpha Star Fund; (F) 20,000 Shares held for the account of Capital Master Fund; and (G) 60,000 shares held for the account of Waterfront Series A Fund. The Shares held by the Magnetar Funds represent approximately 6.96% of the total number of Shares outstanding (calculated pursuant to Rule 13d-3(d)(1)(i)) of the outstanding shares of the Issuer).
(b)	Percent of class: As of June 30, 2026, each of the Reporting Persons were deemed to be the beneficial owner constituting approximately 6.96% of the total number of shares outstanding (based upon the information provided by the Issuer in Form 8K filed on June 10, 2026, there were approximately 28,750,000 Shares outstanding).
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 0
	(ii) Shared power to vote or to direct the vote: 2,000,000
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: 2,000,000
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
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 acquired and are held in the ordinary course of business and 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.

MAGNETAR FINANCIAL LLC

Signature:	/s/ Hayley Stein
Name/Title:	Name:Hayley Stein, Title: Attorney-in-fact for David J. Snyderman, Administrative Manager of Supernova Management LLC
Date:	08/13/2026

MAGNETAR CAPITAL PARTNERS LP

Signature:	/s/ Hayley Stein
Name/Title:	Name:Hayley Stein, Title: Attorney-in-fact for David J. Snyderman, Administrative Manager of Supernova Management LLC
Date:	08/13/2026

SUPERNOVA MANAGEMENT LLC

Signature:	/s/ Hayley Stein
Name/Title:	Name:Hayley Stein, Title: Attorney-in-fact for David J. Snyderman, Administrative Manager of Supernova Management LLC
Date:	08/13/2026

DAVID J. SNYDERMAN

Signature:	/s/ Hayley Stein
Name/Title:	Name:Hayley Stein, Title: Attorney-in-fact for David J. Snyderman, Administrative Manager of Supernova Management LLC
Date:	08/13/2026

Comments accompanying signature: MAGNETAR FINANCIAL LLC BY: Magnetar Capital Partners LP, its Sole Member BY: Supernova Management LLC, its General Partner MAGNETAR CAPITAL PARTNERS LP By: Supernova Management LLC, its General Partner

Exhibit Information

99.1 Joint Filing Agreement, dated as of August 13, 2026, among the Reporting Persons. 99.2 Power of Attorney, dated as of December 22, 2022 filed by the Reporting Persons on August 13, 2026.