Schedule 13G: HOOPP's 0.5% Stake in SilverBox Corp IV (SBXD)

Rhea-AI Filing Summary

Healthcare of Ontario Pension Plan Trust Fund (HOOPP) reports beneficial ownership of 100,000 Class A ordinary shares of SilverBox Corp IV, representing 0.5% of the outstanding Class A shares based on 20,455,000 shares reported by the issuer. The position consists of 99,998 Class A shares plus 2 Class A shares held in units that include one-third of a redeemable warrant; whole warrants are exercisable at $11.50 per share. HOOPP states these securities are held in the ordinary course of business and were not acquired to influence control. HOOPP is a pension plan trust formed under Ontario law and reports sole voting and dispositive power over the 100,000 shares.

Positive

• Clear disclosure of beneficial ownership: 100,000 Class A shares with sole voting and dispositive power
• Detailed composition of the position: 99,998 Class A shares plus 2 Class A shares held in units containing one-third of a redeemable warrant, with warrants exercisable at $11.50
• Certification that the securities are held in the ordinary course of business and not to influence control, enhancing transparency

Negative

• None.

Insights

Financial Analyst

TL;DR: Small passive institutional stake (0.5%) disclosed; unlikely to move valuation but indicates institutional participation.

The filing shows HOOPP holds 100,000 Class A shares with sole voting and dispositive power, representing a 0.5% stake based on the issuer's reported 20,455,000 outstanding Class A shares. The position includes ordinary shares and a small structural element of warrants embedded in units, exercisable at $11.50. Given the size relative to the outstanding base, the holding is not material to control or near-term capital structure; it is a transparent disclosure of an institutional investor's passive position.

Corporate Governance Expert

TL;DR: Filing confirms passive ownership and a certification that holdings are not intended to influence issuer control.

HOOPP explicitly certifies the securities were acquired and are held in the ordinary course of business and not to change or influence control. The reporting person is a pension plan trust organized under Ontario law, and the filing identifies sole voting and dispositive authority for the 100,000 shares. From a governance perspective, this disclosure reinforces transparency but does not signal activist or controlling intent given the sub-5% stake.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

SilverBox Corp IV

(Name of Issuer)

Class A ordinary shares, $0.0001 par value

(Title of Class of Securities)

G81354105

(CUSIP Number)

06/30/2025

(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)

SCHEDULE 13G

CUSIP No. G81354105

1

Names of Reporting Persons

Healthcare of Ontario Pension Plan Trust Fund

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

ONTARIO, CANADA

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 100,000.00
6	Shared Voting Power
7	Sole Dispositive Power 100,000.00
8	Shared Dispositive Power

9

Aggregate Amount Beneficially Owned by Each Reporting Person

100,000.00

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)

0.5 %

12

Type of Reporting Person (See Instructions)

FI

Comment for Type of Reporting Person: In reference to Rows 5, 7 and 9 above, amount consists of 99,998 Class A ordinary shares, $0.0001 par value ("Class A Shares"), of SilverBox Corp IV, a blank check company formed under the laws of the Cayman Islands (the "Issuer"), and 2 Class A Shares held in the form of units, each consisting of one Class A Share and one-third of one redeemable warrant. Each whole warrant entitles the holder thereof to purchase one Class A Share at a price of $11.50 per share, subject to adjustment. In reference to Row 11 above, percentage ownership is based on 20,455,000 Class A Shares issued and outstanding as of May 13, 2025, as reported on the Issuer's quarterly report on Form 10-Q for the quarter ended March 31, 2025, filed with the Securities and Exchange Commission on May 13, 2025.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: SilverBox Corp IV
(b)	Address of issuer's principal executive offices: 1250 S. Capital of Texas Highway, Building 2, Suite 285, Austin, TX 78746
Item 2.
(a)	Name of person filing: Healthcare of Ontario Pension Plan Trust Fund ("HOOPP")
(b)	Address or principal business office or, if none, residence: 1 York Street, Suite 1900, Toronto, Ontario, Canada, M5J 0B6
(c)	Citizenship: Ontario, Canada
(d)	Title of class of securities: Class A ordinary shares, $0.0001 par value
(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).
	A pension plan formed as a trust under the laws of Ontario, Canada and registered with the Financial Services Regulatory Authority of Ontario.
Item 4.	Ownership
(a)	Amount beneficially owned: See Item 9 on page 2.
(b)	Percent of class: See Item 11 on page 2.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: See Item 5 on page 2.
	(ii) Shared power to vote or to direct the vote: See Item 6 on page 2.
	(iii) Sole power to dispose or to direct the disposition of: See Item 7 on page 2.
	(iv) Shared power to dispose or to direct the disposition of: See Item 8 on page 2.
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 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. By signing below I certify that, to the best of my knowledge and belief, the regulatory scheme applicable to a pension plan formed as a trust under the laws of Ontario, Canada and registered with the Financial Services Regulatory Authority of Ontario is substantially comparable to the regulatory scheme applicable to the functionally equivalent U.S. institution(s). I also undertake to furnish to the Securities and Exchange Commission staff, upon request, information that would otherwise be disclosed in a Schedule 13D.

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.

Healthcare of Ontario Pension Plan Trust Fund

Signature:	/s/ Abas Kanu
Name/Title:	VP, HOOPP Compliance Officer
Date:	08/13/2025

FAQ

How many SBXD shares does HOOPP own?

HOOPP beneficially owns 100,000 Class A ordinary shares of SilverBox Corp IV, with sole voting and dispositive power over those shares.

What percentage of SilverBox Corp IV (SBXD) does HOOPP's stake represent?

The reported position represents 0.5% of the Class A shares, based on 20,455,000 Class A shares reported by the issuer.

Does HOOPP's holding include warrants or unit structures?

Yes. The position includes 99,998 Class A shares plus 2 Class A shares held in units that include one-third of a redeemable warrant; whole warrants are exercisable at $11.50 per share.

Is HOOPP attempting to influence control of SBXD?

No. HOOPP certifies the securities were acquired and are held in the ordinary course of business and were not acquired to influence control of the issuer.

Where is the reporting person organized?

The reporting person, Healthcare of Ontario Pension Plan Trust Fund, is a pension plan trust formed under the laws of Ontario, Canada.