[144] Atara Biotherapeutics, Inc. SEC Filing

ATRA submitted a notice for the settlement/sale of 13,887 shares of Common Stock on 05/15/2026, described as settlement of vested RSUs issued under an S-8 registration plan.

Rhea-AI Filing Summary

ATRA submitted a notice for the settlement/sale of 13,887 shares of Common Stock on 05/15/2026, described as settlement of vested RSUs issued under an S-8 registration plan. The excerpt also shows a prior sale of 2,996 shares on 03/02/2026.

Insights

Equity Compensation Analyst

RSU settlement reported; routine issuer-side equity compensation activity.

The filing lists the settlement of 13,887 vested RSUs on 05/15/2026 under an S-8 registration plan, indicating compensation-related issuance rather than an open-market discretionary sale by a third party.

There is a separate line showing a prior disposition of 2,996 shares on 03/02/2026, with an accompanying numeric amount. Subsequent filings would show any resale plans or brokered transactions.

Key Figures

RSU settlement: 13,887 shares Prior sale: 2,996 shares Associated amount: $15,237.36

3 metrics

RSU settlement 13,887 shares Settlement of vested RSUs under S-8 on <date>05/15/2026</date>

Prior sale 2,996 shares Shares sold on <date>03/02/2026</date>

Associated amount <money>$15,237.36</money> Numeric amount listed adjacent to the 2,996-share sale entry

Key Terms

RSU, S-8 registration plan, Form 144

3 terms

RSU financial

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

Restricted stock units (RSUs) are a form of company shares given to employees as part of their compensation, usually with certain restrictions or conditions, such as remaining with the company for a set period. When these restrictions lift, employees receive actual shares that they can sell or hold. For investors, RSUs can impact a company's stock supply and reflect the company's commitment to attracting and retaining talent.

S-8 registration plan regulatory

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

Form 144 regulatory

"Securities To Be Sold / Securities Sold During The Past 3 Months"

Form 144 is a document that investors must file with the government when they plan to sell a large number of shares of a company's stock. It helps ensure transparency so everyone knows how many shares are being sold and when, which can impact the stock's price.

FAQ

What does the Form 144 for ATRA report?

The notice reports the settlement of 13,887 vested RSUs on 05/15/2026 under an S-8 registration plan. It also records a prior sale of 2,996 shares on 03/02/2026, per the excerpt.

Who receives the shares listed as settling on 05/15/2026?

The excerpt describes the transaction as equity compensation for services rendered, indicating the shares are issued to a service recipient upon RSU vesting under the S-8 plan, rather than a third-party market purchase.

Does the filing show proceeds from recent sales by insiders for ATRA?

The excerpt lists a figure of 15237.36 adjacent to a 2,996-share sale dated 03/02/2026. The filing text pairs that number with the prior sale entry, implying a monetary amount tied to that disposition.

Is the 13,887-share settlement part of a registered plan?

Yes. The settlement is described as occurring under an S-8 registration plan, indicating the shares were issued pursuant to an existing employee benefit registration on the issuer’s shelf for compensatory purposes.

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Accepted by SEC EDGAR 05/18/2026 - 04:45 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	5981	62680.88	9371144	05/18/2026	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	05/15/2026	Settlement of vested RSUs issued under an S-8 Registration Plan	Issuer			13887	05/15/2026	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	03/02/2026	2996	15237.36

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	05/18/2026
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/ John Chao, Attorney-in-Fact for AnhCo Nguyen
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)