Definium Therapeutics (DFTX) CEO share sale covers RSU tax withholding

Rhea-AI Filing Summary

Definium Therapeutics, Inc. Chief Executive Officer Robert Barrow reported an open-market sale of 24,431 Common Shares at a weighted average price of $18.47 per share. The shares were sold to satisfy withholding tax obligations linked to vested restricted stock units under a Rule 10b5-1 sell-to-cover plan adopted on June 15, 2022.

Following this transaction, Barrow directly holds 752,454 Common Shares, and this amount includes 1,586 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan. Because the sale was for tax withholding under a pre-planned trading arrangement, it reflects a routine administrative event rather than a discretionary change in ownership.

Insights

Equity compensation and insider-trading analyst

CEO’s reported share sale is a routine tax-withholding event under a pre-set plan.

The filing shows CEO Robert Barrow sold 24,431 Common Shares at a weighted average of $18.47. A footnote explains these shares were sold solely to cover withholding taxes on vested restricted stock units, executed via a pre-established Rule 10b5-1 sell-to-cover plan.

This pattern is typical for equity compensation: shares are automatically sold to fund taxes when restricted stock units vest. After the sale, Barrow still directly holds 752,454 Common Shares, which includes 1,586 shares acquired through the 2024 Employee Share Purchase Plan. Overall, the transaction appears administrative rather than a discretionary change in his exposure.

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)
03/25/2026

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	03/25/2026		S(1)		24,431	D	$18.47(2)	752,454(3)	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. Represents the number of Common Shares sold to satisfy withholding tax obligations in connection with the settlement of vested restricted stock units, pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on June 15, 2022.

2. The reported price is a weighted average sales price. These shares were sold in multiple transactions on March 25, 2026 at prices ranging from $18.36 to $18.80. 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.

3. Amount includes 1,586 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan.

	/s/ Mark Sullivan, Attorney-in-Fact for Robert Barrow	03/26/2026
	** 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)

FAQ

What insider transaction did Definium Therapeutics (DFTX) report for its CEO?

Definium Therapeutics reported that CEO Robert Barrow sold 24,431 Common Shares at a weighted average price of $18.47. According to the filing, the sale was linked to vested restricted stock units and executed as part of a tax-withholding sell-to-cover arrangement.

Why did the Definium Therapeutics (DFTX) CEO sell 24,431 shares?

The CEO sold 24,431 shares to satisfy withholding tax obligations arising from the settlement of vested restricted stock units. The filing states this occurred pursuant to sell-to-cover elections under a pre-adopted Rule 10b5-1 trading plan, indicating a routine compensation-related event.

Was the Definium Therapeutics (DFTX) CEO’s share sale pre-planned?

Yes. The filing notes the tax-withholding sale was made under a Rule 10b5-1 plan adopted on June 15, 2022. Such plans pre-schedule trades, reducing the likelihood that the timing reflects the insider’s short-term view of the stock.

How many Definium Therapeutics (DFTX) shares does the CEO hold after the sale?

After the transaction, CEO Robert Barrow directly holds 752,454 Common Shares of Definium Therapeutics. The filing explains this total includes 1,586 shares that were acquired through the company’s 2024 Employee Share Purchase Plan, reflecting ongoing equity ownership.

At what prices were the Definium Therapeutics (DFTX) shares sold by the CEO?

The reported weighted average sale price was $18.47 per share. A footnote explains that multiple trades occurred on March 25, 2026 at prices ranging from $18.36 to $18.80, and detailed trade breakdowns are available upon request from the company or regulators.

What does the Definium Therapeutics (DFTX) Form 4 say about ESPP participation?

The Form 4 notes that the CEO’s post-transaction holdings include 1,586 shares acquired under the Definium Therapeutics, Inc. 2024 Employee Share Purchase Plan. This indicates participation in the company’s employee share purchase program in addition to equity compensation grants.