[Form 4] Atara Biotherapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Atara Biotherapeutics (ATRA) President and CEO AnhCo Nguyen, who also serves as a director, reported an automatic sale of company common stock related to tax withholding on vested restricted stock units. On 11/17/2025, Nguyen sold 2,859 shares of common stock at a weighted average price of $13.186 per share and an additional 56 shares at a weighted average price of $13.188 per share. These transactions were carried out by a broker as part of a group sale for multiple employees to satisfy withholding tax liabilities tied to equity awards. Following the transactions, Nguyen directly beneficially owned 64,974 shares of Atara Biotherapeutics common stock.

Insider Trade Summary

Net Seller: 2,915 shares ($38,437)

Net Sell 2 txns

Insider Nguyen AnhCo

Role President and CEO

Sold 2,915 shs ($38K)

Type	Security	Shares	Price	Value
Sale	Common Stock	2,859	$13.186	$38K
Sale	Common Stock	56	$13.188	$738.53

Holdings After Transaction: Common Stock — 65,030 shares (Direct)

Footnotes (1)

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. The sale price of the reporting person's shares represents the weighted average price of all shares sold by a broker on November 17, 2025 on behalf of a group of employees of the Issuer to satisfy the payment of withholding tax liability of such employees.

Form 4 Insider Transactions: What Each Field Means →

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
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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)
11/17/2025

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	11/17/2025		S(1)		2,859	D	$13.186(2)	65,030	D
Common Stock	11/17/2025		S(1)		56	D	$13.188(2)	64,974	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 November 17, 2025 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	11/19/2025
	** 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).
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