Sell4

Definium Therapeutics, Inc.

DFTX

Total Value

$721.7K

Net $721.7K sold

Filing Date

Sep 4, 2026

2 transactions

Sales

$721.7K

1 transaction

Trade Summary

On Sep 2, 2026 through Sep 3, 2026, Barrow Robert, Insider, sold $721.7K of Definium Therapeutics, Inc. (DFTX) across 2 transactions. The filing covers Common Shares and reflects net selling of $721.7K. Reported prices ranged from $37.94. Insider transactions are sourced from SEC Form 4 disclosures and should be reviewed alongside company fundamentals and the insider's broader trading history.

Price at the Time of the Trade

DFTX daily price with the insider's sale marked at $37.94.

Sold in the upper half of the 6-month range · about level with today's price.

Price data is delayed and provided for context only — not investment advice.

Insider Information

Name: Barrow Robert
Role: Insider
Location: NEW YORK, NY

Filing Details

Filing Date: Sep 4, 2026
Transaction Date: Sep 2, 2026
Accession Number: 0001193125-26-384042
Form Type: 4
Net Trading Amount: -$721.7K

Non-Derivative Transactions

Date	Security	Shares	Price	Type	Value
Sep 2, 2026	Common Shares	40,000	—	Grant/Award	—
Sep 3, 2026	Common Shares	19,023	$37.94	Sale	$721.7K

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Footnotes

(F1)The common shares represent the first tranche of performance share units granted effective February 3, 2026. Each performance share unit represented a contingent right to receive one common share based on, and subject to, the achievement of certain clinical and regulatory milestones set forth in the Performance Share Unit Award Agreement.
(F2)Amount includes 417 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan on August 17, 2026.
(F3)Represents the number of Common Shares sold to satisfy withholding tax obligations in connection with the settlement of vested performance restricted stock units, pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on June 15, 2022
(F4)The reported price is a weighted average sales price. These shares were sold in multiple transactions on September 3, 2026 at prices ranging from $37.46 to $38.94. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Barrow Robert

(Last)

(First)

(Middle)

C/O DEFINIUM THERAPEUTICS, INC.

ONE WORLD TRADE CENTER, SUITE 8500

(Street)

NEW YORK

10007

(City)

(State)

(Zip)

2. Issuer Name and Ticker or Trading Symbol
Definium Therapeutics, Inc. [ DFTX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chief Executive Officer

3. Date of Earliest Transaction (Month/Day/Year)
09/02/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Shares	09/02/2026		A		40,000⁽¹⁾	A	$0.00	1,513,663⁽²⁾	D
Common Shares	09/03/2026		S⁽³⁾		19,023	D	$37.94⁽⁴⁾	1,494,640	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)

Explanation of Responses:

1. The common shares represent the first tranche of performance share units granted effective February 3, 2026. Each performance share unit represented a contingent right to receive one common share based on, and subject to, the achievement of certain clinical and regulatory milestones set forth in the Performance Share Unit Award Agreement.

2. Amount includes 417 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan on August 17, 2026.

3. Represents the number of Common Shares sold to satisfy withholding tax obligations in connection with the settlement of vested performance restricted stock units, pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on June 15, 2022

4. The reported price is a weighted average sales price. These shares were sold in multiple transactions on September 3, 2026 at prices ranging from $37.46 to $38.94. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

	/s/ Mark Sullivan, Attorney-in-Fact for Robert Barrow	09/04/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

Form 4 as rendered by the SEC from accession 0001193125-26-384042.

Definium Therapeutics, Inc.

Trade Summary

Price at the Time of the Trade

Company Information

Insider Information

Filing Details

Non-Derivative Transactions

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Footnotes

SEC Form 4

SEC Filing

SEC Form 4

Price at the Time of the Trade