DFTX CLO sells 13,008 shares for tax withholding

Definium Therapeutics, Inc. Chief Legal Officer Mark Sullivan reported an open-market sale of 13,008 Common Shares on June 25, 2026 at $45.03 per share.

Rhea-AI Filing Summary

Definium Therapeutics, Inc. Chief Legal Officer Mark Sullivan reported an open-market sale of 13,008 Common Shares on June 25, 2026 at $45.03 per share. According to the footnote, these shares were sold to satisfy withholding tax obligations tied to the settlement of vested restricted stock units under sell-to-cover elections in a Rule 10b5-1 plan adopted on March 14, 2024. Following this transaction, Sullivan directly holds 320,571 Common Shares, indicating a continuing substantial equity position.

Insider Trade Summary 10b5-1

Net Seller: 13,008 shares

Net Sell 1 txn

Insider Sullivan Mark

Role Chief Legal Officer

Sold 13,008 shs ($586K)

Type	Security	Shares	Price	Value
Sale	Common Shares	13,008	$45.03	$586K

Holdings After Transaction: Common Shares — 320,571 shares (Direct)

Footnotes (1)

1. F1. 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 March 14, 2024.

Key Figures

Shares sold: 13,008 shares Sale price: $45.03 per share Shares held after transaction: 320,571 shares +3 more

6 metrics

Shares sold 13,008 shares Open-market sale on June 25, 2026

Sale price $45.03 per share Price for Common Shares sold

Shares held after transaction 320,571 shares Direct ownership after June 25, 2026 sale

Transaction code S Sale in open market or private transaction

Net shares sold 13,008 shares Net-sell direction in transaction summary

10b5-1 plan adoption date March 14, 2024 Plan governing sell-to-cover elections

Key Terms

Rule 10b5-1 plan, sell-to-cover elections, withholding tax obligations, restricted stock units, +1 more

5 terms

Rule 10b5-1 plan regulatory

"pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on March 14, 2024"

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.

sell-to-cover elections financial

"sold to satisfy withholding tax obligations in connection with the settlement of vested restricted stock units, pursuant to sell-to-cover elections"

withholding tax obligations financial

"Common Shares sold to satisfy withholding tax obligations in connection with the settlement of vested restricted stock units"

restricted stock units financial

"in connection with the settlement of vested restricted stock units, pursuant to sell-to-cover elections"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

open-market sale financial

"transaction_action": "open-market sale""

An open-market sale is when a shareholder sells existing shares directly on a public exchange to any willing buyer, rather than through a private deal. Think of it like putting goods on a busy market stall where price is set by supply and demand; for investors it matters because such sales increase available supply, can put short-term downward pressure on the stock price, and signal changes in liquidity or investor confidence.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did Definium Therapeutics (DFTX) report for Mark Sullivan?

Definium Therapeutics reported that Chief Legal Officer Mark Sullivan sold 13,008 Common Shares. The sale occurred on June 25, 2026 at $45.03 per share and was disclosed as an open-market transaction on a Form 4 insider filing.

Why were Mark Sullivan’s Definium Therapeutics (DFTX) shares sold?

The 13,008 shares were sold to satisfy withholding tax obligations. The footnote explains the sale was related to the settlement of vested restricted stock units through sell-to-cover elections under a pre-established Rule 10b5-1 trading plan.

Was Mark Sullivan’s Definium Therapeutics (DFTX) share sale under a Rule 10b5-1 plan?

Yes. The filing states the tax-related share sale was made pursuant to sell-to-cover elections under a Rule 10b5-1 plan adopted on March 14, 2024, indicating the transaction followed a pre-arranged trading schedule.

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

After selling 13,008 Common Shares, Mark Sullivan holds 320,571 Common Shares directly. This post-transaction holding, reported in the Form 4, shows he retains a significant equity stake in Definium Therapeutics.

What price was received for the Definium Therapeutics (DFTX) shares sold?

The 13,008 Common Shares were sold at an average price of $45.03 per share. This price is reported in the Form 4 as the transaction price for the open-market sale executed on June 25, 2026.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 06/26/2026 - 04:30 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^*

Sullivan Mark

(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)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
06/25/2026

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	06/25/2026		S(1)		13,008	D	$45.03	320,571	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 March 14, 2024.

	/s/ Mark Sullivan	06/26/2026
	** 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)