UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 6, 2025

Atara Biotherapeutics, Inc.

(Exact name of Registrant as Specified in Its Charter)


Delaware	001-36548	46-0920988
(State or Other Jurisdiction of Incorporation)	(Commission File Number)	(IRS Employer Identification No.)

1280 Rancho Conejo Blvd
Thousand Oaks, California		91320
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s Telephone Number, Including Area Code: (805) 623-4211

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading
Symbol(s)

Name of each exchange

on which registered

Common Stock, par value $0.0001 per share

ATRA

The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.05

Costs Associated with Exit or Disposal Activities.

On October 6, 2025, Atara Biotherapeutics, Inc. (the “Company”) announced a reduction in its workforce that will impact approximately 29% of its current employees, retaining approximately 15 employees essential to executing on the Company’s strategic priorities. The Company expects to complete the workforce reduction by January 2026. The Company expects to recognize approximately $1.3 million for severance and related benefits for employees laid off under the reduction in force. Approximately fifty percent of these charges are salary continuation payments and wages for the 60-day notice period in accordance with the California Worker Adjustment and Retraining Notification Act. The Company may also incur other charges or cash expenditures not currently contemplated due to events that may occur as a result of, or associated with, the workforce reduction. Additional details will be provided in the Company’s Quarterly Report on Form 10-Q for the period ending September 30, 2025.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

ATARA BIOTHERAPEUTICS, INC.

Date: October 6, 2025

/s/ AnhCo Thieu Nguyen

AnhCo Thieu Nguyen
President and Chief Executive Officer
(Duly Authorized Officer and Principal Executive Officer)

Atara Biotherapeutics, Inc. 8-K