Atara CEO sells 5,062 shares for tax withholding

Atara Biotherapeutics, Inc. (ATRA) reported that President and CEO Nguyen AnhCo had 5,062 shares of common stock sold on August 17, 2026.

Rhea-AI Filing Summary

Atara Biotherapeutics, Inc. (ATRA) reported that President and CEO Nguyen AnhCo had 5,062 shares of common stock sold on August 17, 2026. According to the disclosure, these shares were sold automatically to satisfy tax withholding obligations upon vesting of restricted stock units under a sale-to-cover provision, at a broker-executed weighted average price. Following this transaction, Nguyen AnhCo directly holds 132,775 shares of Atara common stock.

Insider Trade Summary

Net Seller: 5,062 shares

Net Sell 1 txn

Insider Nguyen AnhCo

Role President and CEO

Sold 5,062 shs ($41K)

Type	Security	Shares	Price	Value
Sale	Common Stock F1, F2	5,062	$8.0764	$41K

Holdings After Transaction: Common Stock — 132,775 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 August 17, 2026, on behalf of a group of employees of the Issuer to satisfy the payment of withholding tax liability of such employees.

Key Figures

Shares sold: 5,062 shares of Common Stock Weighted average sale price: $8.0764 per share Shares held after transaction: 132,775 shares of Common Stock

3 metrics

Shares sold 5,062 shares of Common Stock Automatic sale on August 17, 2026 to satisfy tax withholding obligations

Weighted average sale price $8.0764 per share Broker-executed sales on August 17, 2026 for a group of employees

Shares held after transaction 132,775 shares of Common Stock Direct ownership by Nguyen AnhCo following the August 17, 2026 transaction

Key Terms

sale-to-cover provision, withholding tax liability, weighted average price

3 terms

sale-to-cover provision financial

"pursuant to a sale-to-cover provision in the award agreement"

withholding tax liability financial

"to satisfy the payment of withholding tax liability of such employees"

weighted average price financial

"represents the weighted average price of all shares sold by a broker"

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

FAQ

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

What insider transaction did ATRA report for CEO Nguyen AnhCo on August 17, 2026?

ATRA reported that CEO Nguyen AnhCo had 5,062 shares of common stock sold on August 17, 2026 to cover tax withholding obligations related to the vesting of restricted stock units, executed under a sale-to-cover provision.

At what price were Nguyen AnhCo’s ATRA shares sold in this Form 4?

The reported sale price was a weighted average price of $8.0764 per share for all shares sold by a broker on August 17, 2026, on behalf of a group of Atara employees to satisfy their withholding tax liabilities.

How many ATRA shares does CEO Nguyen AnhCo hold after the reported sale?

After the reported transaction, CEO Nguyen AnhCo directly holds 132,775 shares of Atara Biotherapeutics, Inc. common stock, as disclosed in the filing.

Was the August 17, 2026 ATRA insider sale part of a Rule 10b5-1 plan?

The filing’s Rule 10b5-1 checkbox is not checked, and the transaction is described instead as an automatic sale to satisfy tax withholding obligations in connection with vesting restricted stock units.

Why were ATRA shares sold for CEO Nguyen AnhCo according to the Form 4 footnotes?

The footnotes state the shares were sold automatically to satisfy tax withholding obligations arising from the vesting of previously granted restricted stock units, pursuant to a sale-to-cover provision in the award agreement.

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

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Available on EDGAR 08/26/2026 - 07:46 PM Accepted by SEC EDGAR 08/26/2026 - 07:45 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 CALIFORNIA 91320

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/17/2026

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 Stock	08/17/2026		S(1)		5,062	D	$8.0764(2)	132,775	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 17, 2026, on behalf of a group of employees of the Issuer to satisfy the payment of withholding tax liability of such employees.

Remarks:

Exhibit List: Exhibit 24 - Power of Attorney

	/s/ AnhCo Nguyen	08/26/2026
	** 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)