Definium CEO gets 40K shares, sells 19,023

Definium Therapeutics CEO Robert Barrow reported a milestone-based share award and a tax-related sell-to-cover sale executed under a Rule 10b5-1 plan.

Rhea-AI Filing Summary

Definium Therapeutics, Inc. (DFTX) reported that Chief Executive Officer and director Robert Barrow received an award of 40,000 common shares on September 2, 2026, representing the first tranche of performance share units originally granted effective February 3, 2026, which vest based on specified clinical and regulatory milestones. This amount also includes 417 shares acquired under the company’s 2024 Employee Share Purchase Plan on August 17, 2026.

On September 3, 2026, Barrow sold 19,023 common shares to satisfy withholding tax obligations related to 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. The reported weighted average sales price was $37.94 per share, with individual trades executed between $37.46 and $38.94 per share.

Insider Trade Summary 10b5-1

Net Seller: 19,023 shares

Net Sell 2 txns

Insider Barrow Robert

Role Chief Executive Officer

Sold 19,023 shs ($722K)

Type	Security	Shares	Price	Value
Sale	Common Shares F3, F4	19,023	$37.94	$722K
Grant/Award	Common Shares F1, F2	40,000	$0.00	$0.00

Holdings After Transaction: Common Shares — 1,494,640 shares (Direct)

Footnotes (4)

1. 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.
2. F2. Amount includes 417 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan on August 17, 2026.
3. 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
4. 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.

Key Figures

Performance share units settled into common shares: 40,000 shares Sell-to-cover shares sold: 19,023 shares Weighted average sale price: $37.94 per share +2 more

5 metrics

Performance share units settled into common shares 40,000 shares First tranche of performance share units granted effective February 3, 2026, settled on September 2, 2026

Sell-to-cover shares sold 19,023 shares Common shares sold on September 3, 2026 to satisfy withholding tax obligations

Weighted average sale price $37.94 per share Weighted average price for 19,023 shares sold on September 3, 2026

Sale price range $37.46 to $38.94 per share Price range for multiple sale transactions on September 3, 2026

Shares acquired under 2024 Employee Share Purchase Plan 417 shares Common shares acquired on August 17, 2026 under Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan

Key Terms

performance share units, Performance Share Unit Award Agreement, sell-to-cover, Rule 10b5-1 plan, +1 more

5 terms

performance share units financial

"The common shares represent the first tranche of performance share units granted"

Performance share units are a type of company stock award given to employees that depend on the company meeting specific goals or targets. If these goals are achieved, the employee receives shares or the value of shares; if not, they may receive little or no compensation. This aligns employees’ interests with the company's success and encourages performance that benefits investors.

Performance Share Unit Award Agreement financial

"milestones set forth in the Performance Share Unit Award Agreement"

sell-to-cover financial

"pursuant to sell-to-cover elections under a Rule 10b5-1 plan"

Sell-to-cover is when part of newly issued or exercised company stock is immediately sold to pay required taxes and fees, so the recipient keeps the remaining shares. For investors this matters because it reduces the number of shares insiders or employees actually hold after a grant, can create small, routine share sales that aren’t signal of cashing out, and slightly increases share supply on the market—like selling a portion of a paycheck to cover the tax bill.

Rule 10b5-1 plan regulatory

"under a Rule 10b5-1 plan adopted on June 15, 2022"

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

withholding tax obligations financial

"sold to satisfy withholding tax obligations in connection with the settlement"

FAQ

What insider transactions did DFTX CEO Robert Barrow report on this Form 4?

He reported an acquisition of 40,000 common shares on September 2, 2026 from performance share units tied to clinical and regulatory milestones, and a sale of 19,023 common shares on September 3, 2026 to cover withholding taxes on vested performance restricted stock units.

At what prices were the DFTX shares sold by Robert Barrow on September 3, 2026?

The sale of 19,023 common shares used a weighted average price of $37.94 per share. The shares were sold in multiple transactions at prices ranging from $37.46 to $38.94 per share.

Were Robert Barrow’s DFTX share sales made under a Rule 10b5-1 plan?

Yes. The filing states the 19,023-share sale was made to satisfy withholding tax obligations pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on June 15, 2022, and the Form 4 affirms transactions under a Rule 10b5-1 plan.

What is the nature of the 40,000-share award reported by DFTX’s CEO?

The 40,000 common shares represent the first tranche of performance share units granted effective February 3, 2026. Each unit was a contingent right to receive one common share based on achieving specified clinical and regulatory milestones in a Performance Share Unit Award Agreement.

What additional DFTX shares did Robert Barrow acquire under the employee share plan?

The reported amount includes 417 common shares acquired on August 17, 2026 under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan, which are counted within the total reported in the acquisition transaction.

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Available on EDGAR 09/04/2026 - 09:30 PM Accepted by SEC EDGAR 09/04/2026 - 09:30 PM Learn about SEC filing dates

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).

X

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 NEW YORK 10007

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

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

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

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

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

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)
			Code	V	Amount	(A) or (D)	Price
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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

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: SEC 1474 (03-26)