Atara CEO sells 2,996 shares for tax withholding

Atara Biotherapeutics President and CEO Nguyen AnhCo sold 2,996 shares of common stock on March 2, 2026 to cover tax withholding on vested restricted stock units.

Rhea-AI Filing Summary

Atara Biotherapeutics President and CEO Nguyen AnhCo sold 2,996 shares of common stock on March 2, 2026 to cover tax withholding on vested restricted stock units.

The shares were sold in open-market transactions at weighted average prices around $5.08 per share, and he now directly holds 61,978 common shares.

Insider Trade Summary

Net Seller: 2,996 shares

Net Sell 4 txns

Insider Nguyen AnhCo

Role President and CEO

Sold 2,996 shs ($15K)

Type	Security	Shares	Price	Value
Sale	Common Stock	198	$5.079	$1K
Sale	Common Stock	58	$5.08	$294.64
Sale	Common Stock	1,298	$5.086	$7K
Sale	Common Stock	1,442	$5.087	$7K

Holdings After Transaction: Common Stock — 61,978 shares (Direct)

Footnotes (2)

1. F1. Shares sold automatically to satisfy tax withholding obligations in connection with the vesting of previously granted restricted stock units, pursuant to a sale-to-cover provision in the award agreement.
2. F2. The sale price of the reporting person's shares represents the weighted average price of all shares sold by a broker on March 2, 2026 on behalf of a group of employees of the Issuer to satisfy the payment of withholding tax liability of such employees.

FAQ

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

What insider transaction did Atara Biotherapeutics (ATRA) report for Nguyen AnhCo?

Atara Biotherapeutics reported that President and CEO Nguyen AnhCo sold 2,996 shares of common stock on March 2, 2026. These sales were open-market transactions executed to satisfy tax withholding obligations tied to the vesting of previously granted restricted stock units.

Why did Atara Biotherapeutics CEO Nguyen AnhCo sell 2,996 ATRA shares?

The 2,996 ATRA shares were sold automatically to satisfy tax withholding obligations from the vesting of restricted stock units. The transactions followed a sale-to-cover provision in the award agreement rather than a discretionary decision to reduce his economic exposure to the company.

At what price were Nguyen AnhCo’s Atara Biotherapeutics shares sold?

The reported sales occurred at weighted average prices near $5.08 per share, specifically at $5.079, $5.080, $5.086, and $5.087. These prices reflect broker-handled sales on March 2, 2026 for a group of employees covering withholding tax liabilities.

How many Atara Biotherapeutics shares does CEO Nguyen AnhCo own after the sale?

Following the tax-related sales, Nguyen AnhCo directly owns 61,978 shares of Atara Biotherapeutics common stock. This post-transaction balance reflects all four open-market sale entries reported for March 2, 2026 and represents his remaining direct equity position.

Were Nguyen AnhCo’s ATRA share sales discretionary or tax-related?

The sales were tax-related, not discretionary. Footnotes explain the shares were sold automatically under a sale-to-cover provision to satisfy withholding taxes triggered by vesting restricted stock units, rather than representing an elective reduction of his holdings.

How many individual transactions comprised Nguyen AnhCo’s 2,996-share sale of ATRA stock?

The 2,996 shares were sold in four separate open-market transactions on March 2, 2026. Each line item reported a different weighted average sale price, but all were executed as part of a coordinated process to cover withholding tax obligations for equity awards.

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

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Accepted by SEC EDGAR 03/04/2026 - 04:28 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).

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^*

Nguyen AnhCo

(Last) (First) (Middle)

C/O ATARA BIOTHERAPEUTICS, INC.

1280 RANCHO CONEJO BOULEVARD

(Street)

THOUSAND OAKS CA 91320

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Atara Biotherapeutics, Inc. [ ATRA ]

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

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President and CEO

3. Date of Earliest Transaction (Month/Day/Year)
03/02/2026

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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	03/02/2026		S(1)		198	D	$5.079(2)	64,776	D
Common Stock	03/02/2026		S(1)		58	D	$5.08(2)	64,718	D
Common Stock	03/02/2026		S(1)		1,298	D	$5.086(2)	63,420	D
Common Stock	03/02/2026		S(1)		1,442	D	$5.087(2)	61,978	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. Shares sold automatically to satisfy tax withholding obligations in connection with the vesting of previously granted restricted stock units, pursuant to a sale-to-cover provision in the award agreement.

2. The sale price of the reporting person's shares represents the weighted average price of all shares sold by a broker on March 2, 2026 on behalf of a group of employees of the Issuer to satisfy the payment of withholding tax liability of such employees.

	/s/ John Chao, Attorney-in-Fact for AnhCo Nguyen	03/04/2026
	** 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.