CastleKnight group discloses 1.4% Trinseo (TSE) stake in amended 13G

Rhea-AI Filing Summary

Trinseo PLC received an amended ownership report from CastleKnight and related entities. The Schedule 13G/A (Amendment No. 2) shows that CastleKnight Master Fund LP, its affiliated general partners and managers, Weitman Capital LLC, and Aaron Weitman collectively report beneficial ownership of 516,826 ordinary shares, or 1.4% of Trinseo’s ordinary shares.

All reporting persons list zero sole voting and dispositive power and instead report shared voting and shared dispositive power over the same 516,826 shares. They also certify that the securities were not acquired and are not held for the purpose or effect of changing or influencing control of Trinseo, but instead are being reported on a passive basis.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

Trinseo PLC

(Name of Issuer)

Ordinary Shares, par value $0.01 per share

(Title of Class of Securities)

G9059U107

(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. G9059U107

1

Names of Reporting Persons

CastleKnight Master Fund 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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13G

CUSIP No. G9059U107

1

Names of Reporting Persons

CastleKnight Fund GP 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 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13G

CUSIP No. G9059U107

1

Names of Reporting Persons

CastleKnight Management 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 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP No. G9059U107

1

Names of Reporting Persons

CastleKnight Management GP 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 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13G

CUSIP No. G9059U107

1

Names of Reporting Persons

Weitman Capital 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

NEW JERSEY

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13G

CUSIP No. G9059U107

1

Names of Reporting Persons

Aaron Weitman

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 516,826.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 516,826.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

516,826.00

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)

1.4 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Trinseo PLC
(b)	Address of issuer's principal executive offices: 440 East Swedesford Road, Suite 301, Wayne, PA 19087
Item 2.
(a)	Name of person filing: CastleKnight Master Fund LP CastleKnight Fund GP LLC CastleKnight Management LP CastleKnight Management GP LLC Weitman Capital LLC Aaron Weitman
(b)	Address or principal business office or, if none, residence: CastleKnight Master Fund LP Maples Corporate Services Limited P.O. Box 309 Ugland House Grand Cayman KY1-1104 Cayman Islands CastleKnight Fund GP LLC 888 Seventh Avenue, 24th Floor New York, New York 10019 United States of America CastleKnight Management LP 888 Seventh Avenue, 24th Floor New York, New York 10019 United States of America CastleKnight Management GP LLC 888 Seventh Avenue, 24th Floor New York, New York 10019 United States of America Weitman Capital LLC c/o Aaron Weitman c/o CastleKnight Management LP 888 Seventh Avenue, 24th Floor New York, New York 10019 United States of America Aaron Weitman c/o CastleKnight Management LP 888 Seventh Avenue, 24th Floor New York, New York 10019 United States of America
(c)	Citizenship: CastleKnight Master Fund LP - Cayman Islands CastleKnight Fund GP LLC - Delaware CastleKnight Management LP - Delaware CastleKnight Management GP LLC - Delaware Weitman Capital LLC - New Jersey Aaron Weitman - United States
(d)	Title of class of securities: Ordinary Shares, par value $0.01 per share
(e)	CUSIP No.: G9059U107
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: CastleKnight Master Fund LP - 516,826 CastleKnight Fund GP LLC - 516,826 CastleKnight Management LP - 516,826 CastleKnight Management GP LLC - 516,826 Weitman Capital LLC - 516,826 Aaron Weitman - 516,826
(b)	Percent of class: CastleKnight Master Fund LP - 1.4% CastleKnight Fund GP LLC - 1.4% CastleKnight Management LP - 1.4% CastleKnight Management GP LLC - 1.4% Weitman Capital LLC - 1.4% Aaron Weitman - 1.4%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: CastleKnight Master Fund LP - 0 CastleKnight Fund GP LLC - 0 CastleKnight Management LP - 0 CastleKnight Management GP LLC - 0 Weitman Capital LLC - 0 Aaron Weitman - 0
	(ii) Shared power to vote or to direct the vote: CastleKnight Master Fund LP - 516,826 CastleKnight Fund GP LLC - 516,826 CastleKnight Management LP - 516,826 CastleKnight Management GP LLC - 516,826 Weitman Capital LLC - 516,826 Aaron Weitman - 516,826
	(iii) Sole power to dispose or to direct the disposition of: CastleKnight Master Fund LP - 0 CastleKnight Fund GP LLC - 0 CastleKnight Management LP - 0 CastleKnight Management GP LLC - 0 Weitman Capital LLC - 0 Aaron Weitman - 0
	(iv) Shared power to dispose or to direct the disposition of: CastleKnight Master Fund LP - 516,826 CastleKnight Fund GP LLC - 516,826 CastleKnight Management LP - 516,826 CastleKnight Management GP LLC - 516,826 Weitman Capital LLC - 516,826 Aaron Weitman - 516,826
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.
	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. Please see Exhibit B attached hereto.
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 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.

CastleKnight Master Fund LP

Signature:	By: CastleKnight Fund GP LLC, its general partner, By: Weitman Capital LLC, its managing member
Name/Title:	By: /s/ Aaron Weitman / Manager
Date:	02/17/2026

CastleKnight Fund GP LLC

Signature:	By: Weitman Capital LLC, its managing member
Name/Title:	By: /s/ Aaron Weitman / Manager
Date:	02/17/2026

CastleKnight Management LP

Signature:	By: CastleKnight Management GP LLC, its general partner, By: Weitman Capital LLC, its managing member
Name/Title:	By: /s/ Aaron Weitman / Manager
Date:	02/17/2026

CastleKnight Management GP LLC

Signature:	By: Weitman Capital LLC, its managing member
Name/Title:	By: /s/ Aaron Weitman / Manager
Date:	02/17/2026

Weitman Capital LLC

Signature:	By: /s/ Aaron Weitman
Name/Title:	Aaron Weitman / Manager
Date:	02/17/2026

Aaron Weitman

Signature:	By: /s/ Aaron Weitman
Name/Title:	Aaron Weitman
Date:	02/17/2026

Exhibit Information

Material to be Filed as Exhibit: [Exhibit A - Joint Filing Agreement] [Exhibit B - Control Person Identification]

FAQ

What does the CastleKnight Schedule 13G/A disclose about Trinseo (TSE) ownership?

The filing discloses that CastleKnight Master Fund LP and related entities beneficially own 516,826 Trinseo ordinary shares, representing 1.4% of the class. All voting and dispositive authority over these shares is reported as shared rather than sole for each reporting person.

Who are the reporting persons in the Trinseo (TSE) Schedule 13G/A amendment?

The reporting persons are CastleKnight Master Fund LP, CastleKnight Fund GP LLC, CastleKnight Management LP, CastleKnight Management GP LLC, Weitman Capital LLC, and Aaron Weitman. Each reports the same 516,826 Trinseo ordinary shares and a 1.4% beneficial ownership stake in the company.

How much of Trinseo’s stock do the CastleKnight entities report owning?

They report beneficial ownership of 516,826 Trinseo ordinary shares, equal to 1.4% of the outstanding class. For each reporting person, sole voting and dispositive power is listed as zero, while shared voting and shared dispositive power cover the full 516,826 shares.

Is the CastleKnight position in Trinseo (TSE) considered passive or activist?

The position is certified as passive. The reporting persons state the securities were not acquired and are not held to change or influence control of Trinseo, and are not held in connection with any transaction intended to have that control-changing purpose or effect.

Why is the CastleKnight Trinseo holding reported on Schedule 13G/A instead of 13D?

Schedule 13G/A is used for certain passive holders. Here, the reporting group certifies the shares were not acquired and are not held to change or influence control of Trinseo, which aligns with using the short-form, passive beneficial ownership report instead of a control-focused Schedule 13D.

What is the significance of Item 5 stating ownership of 5 percent or less for Trinseo (TSE)?

Item 5 confirms the group’s beneficial ownership is 5% or less of Trinseo’s outstanding ordinary shares. In this amendment, the reported stake is 1.4%, which places the CastleKnight-related holders below the typical 5% threshold often associated with larger strategic or activist positions.