Adage Capital discloses 6.4% Bain Capital GSS (BCSS) ownership in 13G filing

Rhea-AI Filing Summary

Adage Capital Management and two principals have disclosed a significant stake in Bain Capital GSS Investment Corp. Class A Ordinary Shares. They report beneficial ownership of 3,000,000 Class A Ordinary Shares, representing 6.40% of the class, based on 46,900,000 shares outstanding as of November 13, 2025, as stated in the company’s Form 10-Q.

Adage Capital Management, L.P., along with Robert Atchinson and Phillip Gross, report shared voting and shared dispositive power over all 3,000,000 shares, with no sole voting or dispositive power. They certify the shares were acquired and are held in the ordinary course of business, not for the purpose or effect of changing or influencing control of the company.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Bain Capital GSS Investment Corp.

(Name of Issuer)

Class A Ordinary Shares, $0.0001 par value

(Title of Class of Securities)

G0R78B106

(CUSIP Number)

12/31/2025

(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. G0R78B106

1

Names of Reporting Persons

Adage Capital Management, L.P.

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 3,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 3,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,000,000.00

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)

6.40 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP No. G0R78B106

1

Names of Reporting Persons

Robert Atchinson

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 3,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 3,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,000,000.00

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)

6.40 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

CUSIP No. G0R78B106

1

Names of Reporting Persons

Phillip Gross

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 3,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 3,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,000,000.00

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)

6.40 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Bain Capital GSS Investment Corp.
(b)	Address of issuer's principal executive offices: 200 Clarendon Street, Boston, MA 02116
Item 2.
(a)	Name of person filing: This statement is filed by: (i) Adage Capital Management, L.P., a Delaware limited partnership ("ACM"), as the investment manager of Adage Capital Partners, L.P., a Delaware limited partnership ("ACP"), with respect to the Class A ordinary shares, $0.0001 par value ("Class A Ordinary Shares") of Bain Capital GSS Investment Corp., a Cayman Islands exempted company (the "Company") directly held by ACP; (ii) Robert Atchinson ("Mr. Atchinson"), as (1) managing member of Adage Capital Advisors, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACA"), managing member of Adage Capital Partners GP, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACPGP"), general partner of ACP and (2) managing member of Adage Capital Partners LLC, a Delaware limited liability company ("ACPLLC"), general partner of ACM, with respect to the Class A Ordinary Shares directly held by ACP; and (iii) Phillip Gross ("Mr. Gross"), as (1) managing member of ACA, managing member of ACPGP and (2) managing member of ACPLLC, general partner of ACM, with respect to the Class A Ordinary Shares directly held by ACP. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party. The filing of this statement should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of the securities reported herein.
(b)	Address or principal business office or, if none, residence: The address of the business office of each of the Reporting Persons is 200 Clarendon Street, 52nd Floor, Boston, Massachusetts 02116.
(c)	Citizenship: ACM is a limited partnership organized under the laws of the State of Delaware. Messrs. Gross and Atchinson are citizens of the United States.
(d)	Title of class of securities: Class A Ordinary Shares, $0.0001 par value
(e)	CUSIP No.: G0R78B106
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: The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentage set forth in this Schedule 13G is calculated based upon an aggregate of 46,900,000 Class A Ordinary Shares outstanding as of November 13, 2025, as reported in the Company's Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2025, filed with the Securities and Exchange Commission on November 14, 2025.
(b)	Percent of class: 6.40%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(ii) Shared power to vote or to direct the vote: The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iii) Sole power to dispose or to direct the disposition of: The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iv) Shared power to dispose or to direct the disposition of: The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
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.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. See Item 2(a).
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.

Adage Capital Management, L.P.

Signature:	/s/ Robert Atchinson
Name/Title:	By: Adage Capital Partners LLC, its General Partner, By: Robert Atchinson, its Managing Member
Date:	02/12/2026

Robert Atchinson

Signature:	/s/ Robert Atchinson
Name/Title:	Robert Atchinson, individually
Date:	02/12/2026

Phillip Gross

Signature:	/s/ Phillip Gross
Name/Title:	Phillip Gross, individually
Date:	02/12/2026

Exhibit Information

Exhibit 99.1: Joint Filing Agreement

FAQ

How much of Bain Capital GSS Investment Corp. (BCSS) does Adage Capital own?

Adage Capital and its principals report beneficial ownership of 3,000,000 Class A Ordinary Shares of Bain Capital GSS Investment Corp., representing 6.40% of the outstanding class, based on 46,900,000 shares outstanding as of November 13, 2025.

Who are the reporting persons in the BCSS Schedule 13G filing?

The Schedule 13G lists Adage Capital Management, L.P., along with individuals Robert Atchinson and Phillip Gross, as reporting persons. They are associated with various Adage-related entities that manage and control the investment holding the Class A Ordinary Shares.

What type of securities of BCSS are reported in this Schedule 13G?

The filing covers Class A Ordinary Shares, $0.0001 par value of Bain Capital GSS Investment Corp. These shares are identified by CUSIP G0R78B106 and represent the equity stake disclosed by the reporting persons.

Do the Adage reporting persons have sole or shared voting power over BCSS shares?

The reporting persons state they have 0 shares with sole voting power and 3,000,000 shares with shared voting power. They also report shared dispositive power over the same 3,000,000 Class A Ordinary Shares and no sole dispositive power.

On what share count is the 6.40% BCSS ownership calculation based?

The 6.40% ownership figure is calculated using 46,900,000 Class A Ordinary Shares outstanding as of November 13, 2025, as reported in Bain Capital GSS Investment Corp.’s Form 10-Q for the quarter ended September 30, 2025.

Is Adage’s BCSS stake intended to influence control of the company?

The reporting persons certify the BCSS shares were acquired and are held in the ordinary course of business and not for the purpose or effect of changing or influencing control of the issuer, consistent with a passive investment under Schedule 13G.