Picton Mahoney files 13G/A for GP-ACT III (4.78%)

Picton Mahoney Asset Management amended a Schedule 13G to report beneficial ownership of 1,375,000 Class A ordinary shares of GP-ACT III ACQUISITION CORP, equal to 4.78% of the class.

Rhea-AI Filing Summary

Picton Mahoney Asset Management amended a Schedule 13G to report beneficial ownership of 1,375,000 Class A ordinary shares of GP-ACT III ACQUISITION CORP, equal to 4.78% of the class. The filing cites 28,750,000 Class A ordinary shares as of March 26, 2026 from the issuer's Form 10-K and is certified on 04/27/2026.

Insights

Institutional Compliance Officer

Amendment clarifies ownership and regulatory parity for a Canadian manager.

Picton Mahoney's 13G/A updates its beneficial ownership to 1,375,000 shares, representing 4.78% of Class A ordinary shares based on the issuer's reported 28,750,000 shares as of March 26, 2026.

The filing includes a certification about the foreign regulatory scheme's comparability and a promise to provide Schedule 13D-equivalent information if requested by staff; this is a routine disclosure step for passive institutional holders.

Key Figures

Beneficial ownership: 1,375,000 shares Percent of class: 4.78% Shares outstanding used for calculation: 28,750,000 shares +2 more

5 metrics

Beneficial ownership 1,375,000 shares Amount beneficially owned reported on Schedule 13G/A

Percent of class 4.78% Percent of Class A ordinary shares as reported in the filing

Shares outstanding used for calculation 28,750,000 shares Class A ordinary shares as of March 26, 2026 (issuer's Form 10-K cited in comment)

Filing certification date 04/27/2026 Signature date by General Counsel & CCO certifying the Schedule 13G/A

CUSIP G4035N103 CUSIP for Class A Ordinary Shares listed on the filing

Key Terms

Schedule 13G/A, Beneficial ownership, Sole dispositive power, Ownership of 5 Percent or Less of a Class

4 terms

Schedule 13G/A regulatory

"Amendment No. 1 GP-ACT III ACQUISITION CORP Class A Ordinary Shares"

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.

Beneficial ownership financial

"Amount beneficially owned: 1375000 Percent of class: 4.78 %"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

Sole dispositive power regulatory

"Sole power to dispose or to direct the disposition of: 1375000"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

Ownership of 5 Percent or Less of a Class regulatory

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

FAQ

What stake did Picton Mahoney report in GPAT?

Picton Mahoney reported beneficial ownership of 1,375,000 shares (4.78%). The percentage is calculated using 28,750,000 Class A shares as of March 26, 2026 cited in the filing's comment referencing the issuer's Form 10-K.

Does this Schedule 13G/A indicate active control of GP-ACT III?

No. The filing classifies the position as passive, noting "Ownership of 5 percent or Less of a Class." The statement lists sole voting and dispositive power amounts but does not claim control or intent to influence management.

When was the ownership percentage based on the issuer's share count?

The filing ties the percentage to 28,750,000 Class A ordinary shares as of March 26, 2026. That share count is cited from the issuer's Form 10-K and used to calculate the reported 4.78% stake.

Who certified the Schedule 13G/A and when?

The filing was certified by Catrina Duong, General Counsel & Chief Compliance Officer, with the signature dated 04/27/2026. The certification affirms the accuracy of the information and a comparability statement about the foreign regulatory scheme.

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Accepted by SEC EDGAR 04/27/2026 - 11:05 AM 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)

GP-ACT III ACQUISITION CORP

(Name of Issuer)

Class A Ordinary Shares

(Title of Class of Securities)

G4035N103

(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): G4035N103

1

Names of Reporting Persons

Picton Mahoney Asset Management

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

CANADA (FEDERAL LEVEL)

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,375,000.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,375,000.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,375,000.00

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)

4.78 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Based on 28,750,000 Class A ordinary shares as of March 26, 2026, reported on issuer's Form 10-K, filed March 26, 2026.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: GP-ACT III ACQUISITION CORP
(b)	Address of issuer's principal executive offices: 300 Park Avenue, 2ND FLOOR, New York, NEW YORK, 10022
Item 2.
(a)	Name of person filing: Picton Mahoney Asset Management
(b)	Address or principal business office or, if none, residence: 33 YONGE STREET, SUITE 320
(c)	Citizenship: Canada
(d)	Title of class of securities: Class A Ordinary Shares
(e)	CUSIP No.: G4035N103
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).
	Investment Fund Manager
Item 4.	Ownership
(a)	Amount beneficially owned: 1375000
(b)	Percent of class: 4.78 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1375000
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1375000
	(iv) Shared power to dispose or to direct the disposition of: 0
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 foreign regulatory scheme applicable to [insert particular category of institutional investor] is substantially comparable to the regulatory scheme applicable to the functionally equivalent U.S. institution(s). I also undertake to furnish to the 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.

Picton Mahoney Asset Management

Signature:	Catrina Duong
Name/Title:	General Counsel & Chief Compliance Officer
Date:	04/27/2026

Comments accompanying 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.