Atara Biotherapeutics (ATRA) employee plans 5,062-share tax sale

Rhea-AI Filing Summary

Atara Biotherapeutics, Inc. (ATRA) is named as the issuer in a Form 144 filed on behalf of employee Nguyen AnhCo, indicating an intent to sell 5,062 shares of common stock through Morgan Stanley Smith Barney. The notice ties the shares to vested RSUs issued under an S-8 equity plan, with a portion sold automatically to satisfy tax withholding obligations under a sale-to-cover provision. The filing also reports a prior sale of shares within the last three months.

Key Figures

Shares to be sold: 5,062 shares of common stock Aggregate market value of shares to be sold: $42,318.32 Shares outstanding: 10,084,272 shares +5 more

8 metrics

Shares to be sold 5,062 shares of common stock Number of shares indicated for sale through Morgan Stanley Smith Barney

Aggregate market value of shares to be sold $42,318.32 Aggregate market value associated with the 5,062 shares to be sold

Shares outstanding 10,084,272 shares Number of Atara Biotherapeutics, Inc. common shares outstanding

Shares acquired as equity compensation 13,887 shares Shares from settlement of vested RSUs on 08/15/2026 as equity compensation

Shares sold in past 3 months 5,241 shares Shares of common stock sold on 05/18/2026

Proceeds from past 3-month sale $47,857.98 Value of shares sold on 05/18/2026

Approximate date of sale 08/17/2026 Approximate sale date listed for the 5,062 shares

Date of RSU settlement 08/15/2026 Date tied to settlement of vested RSUs issued under an S-8 plan

Key Terms

Rule 144, restricted stock units, sale-to-cover, S-8 Registration Plan, +1 more

5 terms

Rule 144 regulatory

"See the definition of "person" in paragraph (a) of Rule 144."

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

restricted stock units financial

"vesting of previously granted restricted stock units, pursuant to a sale-to-cover"

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 financial

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

S-8 Registration Plan regulatory

"Settlement of vested RSUs issued under an S-8 Registration Plan"

equity compensation financial

"Equity compensation for services rendered"

Equity compensation is pay given to employees, executives or contractors in the form of company ownership—such as stock, stock options or restricted shares—rather than just cash. It matters to investors because it can align workers' incentives with shareholders (like paying someone in slices of the same pie they help grow), but it also increases the number of shares outstanding and company expenses, affecting ownership percentages and earnings per share.

FAQ

What does the Form 144 filing involving ATRA disclose?

The Form 144 discloses that Nguyen AnhCo may sell 5,062 shares of Atara Biotherapeutics, Inc. (ATRA) common stock through Morgan Stanley Smith Barney, related to vested restricted stock units under an S-8 equity compensation plan.

How many ATRA shares are covered by the potential sale in this Form 144?

The notice covers a potential sale of 5,062 shares of Atara Biotherapeutics, Inc. common stock, with an indicated aggregate market value of $42,318.32 at the time of the filing details.

What is the source of the ATRA shares to be sold under this Form 144?

The shares are tied to the settlement of vested restricted stock units issued under an S-8 Registration Plan, described as equity compensation for services rendered by Nguyen AnhCo.

Were there any prior ATRA stock sales by this person in the last three months?

Yes. The Form 144 reports that on 05/18/2026, 5,241 shares of Atara Biotherapeutics, Inc. common stock were sold for $47,857.98 during the prior three-month period.

How many ATRA shares are reported as outstanding in this Form 144?

The filing lists 10,084,272 shares of Atara Biotherapeutics, Inc. common stock as outstanding, providing a context figure alongside the intended sale amount.

What is the stated purpose of the ATRA share sale related to this Form 144?

The remarks state that shares are being sold automatically to satisfy tax withholding obligations in connection with the vesting of previously granted restricted stock units, under a sale-to-cover provision in the award agreement.

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Available on EDGAR 08/26/2026 - 07:48 PM Accepted by SEC EDGAR 08/26/2026 - 07:47 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001977970
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	Atara Biotherapeutics, Inc.
SEC File Number	001-36548
Address of Issuer	c/o Atara Biotherapeutics, Inc. 1280 Rancho Conejo Boulevard Thousand Oaks CALIFORNIA 91320
Phone	805-623-4211
Name of Person for Whose Account the Securities are To Be Sold	Nguyen AnhCo
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Director
Relationship to Issuer	Officer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common Stock	Morgan Stanley Smith Barney LLC Executive Services 200 W Civic Center Drive, 4th Floor Sandy UT 84070	5062	42318.32	10084272	08/17/2026	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common Stock	08/15/2026	Settlement of vested RSUs issued under an S-8 Registration Plan	Issuer			13887	08/15/2026	Equity compensation for services rendered

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
AnhCo Nguyen 1280 Rancho Conejo Boulevard Thousand Oaks CA 91320	Common Stock	05/18/2026	5241	47857.98

144: Remarks and Signature

Remarks	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.
Date of Notice	08/26/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ AnhCo Nguyen
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)