[Form 4] Atara Biotherapeutics, Inc Insider Trading Activity

Rhea-AI Filing Summary

AnhCo Nguyen, who is listed as President and CEO and a director of Atara Biotherapeutics, reported automatic sales of company common stock on 08/18/2025 to satisfy tax withholding associated with vested restricted stock units. Three sale entries total 2,958 shares disposed at weighted-average prices of approximately $11.613–$11.617 per share, leaving the reporting person with 67,889 shares beneficially owned after the transactions. The filing notes the sales were executed by a broker pursuant to a sale-to-cover provision in the award agreement and that the reported sale price is a weighted average across employees whose shares were sold.

Insights

Corporate Governance Expert

TL;DR: Routine sale-to-cover for RSU tax withholding by a CEO and director; not a sign of unusual insider activity.

This Form 4 reports automatic disposals tied to tax withholding from vested restricted stock units rather than voluntary market sales. The transactions are described as broker-executed sale-to-cover events and the aggregate number of shares (2,958) is small relative to the reported post-transaction holding (67,889 shares). From a governance perspective, these transactions follow standard equity compensation mechanics and include explanatory language satisfying disclosure expectations.

Securities Analyst

TL;DR: Sales were mechanistic to satisfy withholding; impact on float and valuation is immaterial.

The filing shows three disposition entries on the same date with weighted-average sale prices around $11.61 per share. These sales were used to satisfy tax liabilities on vested RSUs and were executed by a broker on behalf of multiple employees, which explains the weighted-average pricing note. The residual beneficial ownership remains substantial for the reporting person, indicating no material change in insider ownership concentration from these transactions.

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

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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)
08/18/2025

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	08/18/2025		S(1)		57	D	$11.613(2)	70,790	D
Common Stock	08/18/2025		S(1)		1,281	D	$11.615(2)	69,509	D
Common Stock	08/18/2025		S(1)		1,620	D	$11.617(2)	67,889	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 August 18, 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	08/20/2025
	** 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).
** 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.
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FAQ

What did the Atara (ATRA) Form 4 filed by AnhCo Nguyen report?

The Form 4 reported automatic sales of 2,958 shares on 08/18/2025 to satisfy tax withholding from vested RSUs, leaving 67,889 shares beneficially owned.

Why were shares sold in the Atara (ATRA) Form 4 transaction?

The shares were sold pursuant to a sale-to-cover provision to pay withholding taxes tied to the vesting of restricted stock units.

What prices were reported for the shares sold in the ATRA Form 4?

The filing reports weighted-average sale prices of approximately $11.613 to $11.617 per share for the broker-executed transactions.

What is AnhCo Nguyen's role at Atara as stated in the Form 4?

AnhCo Nguyen is identified as President and CEO and a director of Atara Biotherapeutics.

How many shares did AnhCo Nguyen own after the reported transactions?

After the reported transactions the Form 4 shows 67,889 shares beneficially owned by the reporting person.