W. R. Berkley reports 1.51M shares (7.4%) of SilverBox

Rhea-AI Filing Summary

W. R. Berkley Corporation filed an amendment (Schedule 13G/A) reporting beneficial ownership of 1,514,573 Class A Ordinary Shares of SilverBox Corp. The filing lists this holding as 7.4% of the class and shows shared voting and shared dispositive power over 1,514,573 shares. The filing is signed by Richard M. Baio on 05/07/2026.

Insights

Institutional Ownership Analyst

Large passive stake reported: 1,514,573 shares (7.4%).

The amendment discloses that W. R. Berkley Corporation beneficially owns 1,514,573 Class A shares, representing 7.4% of the class, with shared voting and dispositive power. The schedule format and shared controls suggest ownership through an affiliated entity rather than sole control.

Key items to watch in subsequent filings include any changes to voting power or conversions that alter percentage ownership; future amendments will reflect material shifts in holdings.

Key Figures

Beneficial ownership: 1,514,573 shares Percent of class: 7.4% Shared voting power: 1,514,573 shares +2 more

5 metrics

Beneficial ownership 1,514,573 shares Amount beneficially owned reported in Item 4

Percent of class 7.4% Percent of class reported in Item 4

Shared voting power 1,514,573 shares Shared power to vote reported in Item 4

Shared dispositive power 1,514,573 shares Shared power to dispose reported in Item 4

Signature date 05/07/2026 Signing date for the amendment

Key Terms

Schedule 13G/A, Beneficially owned, Shared dispositive power

3 terms

Schedule 13G/A regulatory

"filed an amendment (Schedule 13G/A) reporting beneficial ownership"

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.

Beneficially owned financial

"Amount beneficially owned: 1,514,573"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Shared dispositive power regulatory

"Shared power to dispose or to direct the disposition of: 1,514,573"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stake does W. R. Berkley Corporation hold in SilverBox Corp (SBXD)?

W. R. Berkley Corporation beneficially owns 1,514,573 Class A Ordinary Shares, representing 7.4% of the class according to this amendment. The filing shows shared voting and dispositive power over the same 1,514,573 shares.

Who signed the Schedule 13G/A amendment for SBXD?

The amendment is signed by Richard M. Baio, identified as Executive Vice President and Chief Financial Officer, and as Executive Vice President and Treasurer, with signature dates of 05/07/2026 on the filing.

Does the filing indicate sole voting or dispositive power over the shares?

No. The filing reports 0 shares as sole voting power and sole dispositive power, and reports 1,514,573 shares as shared voting power and shared dispositive power, per the Item 4 breakdown.

Is the 1,514,573 share amount the total reported as beneficially owned?

Yes. Item 4 lists the amount beneficially owned as 1,514,573 shares and the percent of class as 7.4%, which are the headline ownership figures disclosed in this amendment.

What entity filed the Schedule 13G/A for SBXD and where is it located?

The filer is W. R. Berkley Corporation, with a principal business address at 475 Steamboat Road, Greenwich, CT 06830, as shown in Item 2 of the amendment.

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

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Accepted by SEC EDGAR 05/08/2026 - 04:07 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)

SILVERBOX CORP IV

(Name of Issuer)

Class A Ordinary Shares, par value $0.0001 per share

(Title of Class of Securities)

G81354105

(CUSIP Number)

03/31/2026

(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): G81354105

1

Names of Reporting Persons

W. R. Berkley Corporation

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 1,514,573.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,514,573.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,514,573.00

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)

7.4 %

12

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13G

CUSIP Number(s): G81354105

1

Names of Reporting Persons

Berkley Insurance Company

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 1,514,573.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,514,573.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,514,573.00

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)

7.4 %

12

Type of Reporting Person (See Instructions)

CO, IC

SCHEDULE 13G

Item 1.
(a)	Name of issuer: SILVERBOX CORP IV
(b)	Address of issuer's principal executive offices: 8701 Bee Cave Road, East Building, Suite 310, Austin, Texas, 78746
Item 2.
(a)	Name of person filing: W. R. Berkley Corporation
(b)	Address or principal business office or, if none, residence: 475 Steamboat Road Greenwich, CT 06830
(c)	Citizenship: US
(d)	Title of class of securities: Class A Ordinary Shares, par value $0.0001 per share
(e)	CUSIP No.: G81354105
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: 1,514,573
(b)	Percent of class: 7.4 %
(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: 1,514,573
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: 1,514,573
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.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. See Exhibit 99.1
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.

W. R. Berkley Corporation

Signature:	/s/ Richard M. Baio
Name/Title:	Richard M. Baio/Executive Vice President and Chief Financial Officer
Date:	05/07/2026

Berkley Insurance Company

Signature:	/s/ Richard M. Baio
Name/Title:	Richard M. Baio/Executive Vice President and Treasurer
Date:	05/07/2026