Atara CEO sells shares to cover tax withholding

Atara Biotherapeutics President and CEO Nguyen AnhCo reported an automatic sale of common stock tied to equity compensation.

Rhea-AI Filing Summary

Atara Biotherapeutics President and CEO Nguyen AnhCo reported an automatic sale of common stock tied to equity compensation. On May 18, 2026, 5,241 shares of common stock were sold at a weighted average price of $9.1289 per share. According to the disclosure, the shares were sold automatically to satisfy tax withholding obligations triggered by the vesting of previously granted restricted stock units under a sale-to-cover provision, rather than as a discretionary open-market sale for portfolio reasons. Following this transaction, AnhCo directly holds 137,837 shares of Atara common stock.

Insider Trade Summary

Net Seller: 5,241 shares

Net Sell 1 txn

Insider Nguyen AnhCo

Role President and CEO

Sold 5,241 shs ($48K)

Type	Security	Shares	Price	Value
Sale	Common Stock	5,241	$9.1289	$48K

Holdings After Transaction: Common Stock — 137,837 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. Represents the weighted average price. The shares were sold in multiple transactions at prices ranging from $9.12 to $9.40, inclusive. The Reporting Person undertakes to provide to the Issuer, any securityholder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above.

Key Figures

Shares sold: 5,241 shares Weighted average sale price: $9.1289 per share Post-transaction holdings: 137,837 shares +1 more

4 metrics

Shares sold 5,241 shares Automatic sale on May 18, 2026 to cover tax withholding

Weighted average sale price $9.1289 per share Common stock sold in multiple transactions

Post-transaction holdings 137,837 shares Common stock directly held by CEO after sale

Sale price range $9.12–$9.40 per share Range of prices for multiple sale transactions

Key Terms

restricted stock units, sale-to-cover provision, weighted average price, open-market sale

4 terms

restricted stock units financial

"in connection with the vesting of previously granted restricted stock units, pursuant to a sale-to-cover provision"

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.

sale-to-cover provision financial

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

weighted average price financial

"Represents the weighted average price. The shares were sold in multiple transactions"

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.

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 Atara Biotherapeutics (ATRA) report for its CEO?

Atara Biotherapeutics reported that President and CEO Nguyen AnhCo sold 5,241 shares of common stock. The sale was automatic to cover tax withholding from vesting restricted stock units under a sale-to-cover provision.

At what price were the Atara (ATRA) CEO’s shares sold in this Form 4?

The CEO’s shares were sold at a weighted average price of $9.1289 per share. The sales occurred in multiple trades within a price range from $9.12 to $9.40 per share.

Why did the Atara (ATRA) CEO sell 5,241 shares according to this filing?

The filing states the 5,241 shares were sold automatically to satisfy tax withholding obligations. This was in connection with the vesting of previously granted restricted stock units under a sale-to-cover provision in the award agreement.

How many Atara Biotherapeutics (ATRA) shares does the CEO hold after this transaction?

After the reported sale, President and CEO Nguyen AnhCo directly holds 137,837 shares of Atara common stock. This figure reflects his position immediately following the 5,241-share sale for tax withholding.

Is the Atara (ATRA) CEO’s Form 4 sale a routine tax transaction?

Yes. The filing explains the shares were sold automatically to cover tax withholding on vesting restricted stock units. Such sale-to-cover transactions are typically routine and tied to compensation-related tax obligations rather than discretionary selling.

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

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Accepted by SEC EDGAR 05/20/2026 - 05:24 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)
05/18/2026

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	05/18/2026		S(1)		5,241	D	$9.1289(2)	137,837	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. Represents the weighted average price. The shares were sold in multiple transactions at prices ranging from $9.12 to $9.40, inclusive. The Reporting Person undertakes to provide to the Issuer, any securityholder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above.

	/s/ John Chao, Attorney-in-Fact for AnhCo Nguyen	05/20/2026
	** 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)