Redmile adjusts Atara Biotherapeutics (ATRA) ownership after warrant exercises

Rhea-AI Filing Summary

Atara Biotherapeutics, Inc. is the subject of an amended Schedule 13D/A filed by Redmile Group, LLC and related entities, updating their ownership after a warrant exercise. The reporting group may be deemed to beneficially own 950,994 shares of Atara common stock, representing 9.9% of the outstanding class.

The position consists of 636,852 shares held by Redmile-managed funds plus 314,142 shares issuable upon exercise of pre-funded warrants, capped by a 9.99% Beneficial Ownership Limitation. On July 16, 2026, Redmile effected a cashless exercise of certain warrants, leading to the issuance of 174,247 shares to Redmile Biopharma Investments II, L.P. and 20,904 shares to Redmile Strategic Long Only Trading Sub, Ltd., with small share amounts withheld to cover the exercise price. Redmile Strategic Long Only Trading Sub, Ltd. is reported to have ceased being a 5% beneficial owner on July 22, 2026.

Filing Explained

Redmile’s 9.9% reported stake includes 314,142 warrant shares, while warrants cover up to 3,217,632 shares subject to the ownership cap.

This Schedule 13D/A reports that Redmile completed a cashless exercise on July 16: Atara issued 195,151 common shares and withheld 60 shares to cover the exercise price. Redmile’s reported beneficial ownership is now 950,994 shares, or 9.9%, including shares that remain issuable under warrants.

Because additional shares increase the total share count, the 195,151 issued shares reduce existing holders’ percentage ownership absent offsetting changes. The filing therefore describes an issuance that has occurred, not merely a registration or future offer.

The reported position consists of 636,852 shares already held and 314,142 shares issuable upon warrant exercise under a 9.99% beneficial ownership limitation. Separately, the Redmile funds hold warrants that the filing says could be exercised into 3,217,632 shares, subject to that limitation.

RBI II reported 631,020 shares, or 6.6%, while Redmile Long Only reported 401,901 shares, or 4.2%, and ceased to be a 5% beneficial owner on July 22. The remaining warrant capacity and the 9.99% limitation are the specific items that determine how the reported position can change in later filings.

Key Figures

Beneficially owned shares: 950,994 shares Ownership percentage: 9.9 % Shares currently held: 636,852 shares +5 more

8 metrics

Beneficially owned shares 950,994 shares Aggregate shares of Atara common stock that may be deemed beneficially owned by the reporting persons

Ownership percentage 9.9 % Percent of Atara common stock class represented by 950,994 shares

Shares currently held 636,852 shares Common shares held by Redmile-managed funds, including RBI II and Redmile Long Only

Shares issuable under limitation 314,142 shares Maximum common shares issuable upon warrant exercise under the 9.99% Beneficial Ownership Limitation

Total warrant underlying shares 3,217,632 shares Common shares issuable upon exercise of all reported warrants held by Redmile-managed funds

Shares issued to RBI II 174,247 shares Common shares issued to Redmile Biopharma Investments II, L.P. upon cashless warrant exercise on July 16, 2026

Shares issued to Redmile Long Only 20,904 shares Common shares issued to Redmile Strategic Long Only Trading Sub, Ltd. upon cashless warrant exercise on July 16, 2026

Shares outstanding baseline 9,010,172 shares Atara common shares outstanding as of May 8, 2026, used in the ownership percentage calculation

Key Terms

Schedule 13D, pre-funded warrants, cashless exercise, Beneficial Ownership Limitation, +1 more

5 terms

Schedule 13D regulatory

"This Amendment No. 3 to (this "Amendment") amends and supplements the filed"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

pre-funded warrants financial

"This Amendment reports the exercise of certain pre-funded warrants to purchase Common Stock"

Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.

cashless exercise financial

"exercised certain Warrants held by RBI II and Redmile Long Only through a "cashless exercise""

A cashless exercise is a way for an option holder to convert stock options into actual shares without paying the purchase price in cash; instead they immediately give up a portion of the newly issued shares to cover the cost and any withholding taxes. Investors care because this process increases the number of shares available and can slightly dilute existing holdings, while also signaling how insiders or employees are realizing compensation without needing cash — similar to paying for a purchase by handing over part of what you just bought.

Beneficial Ownership Limitation regulatory

"which is the maximum number of shares of Common Stock that could be issued upon exercise of the Warrants under the 9.99% beneficial ownership limitation (the "Beneficial Ownership Limitation")"

A beneficial ownership limitation is a rule that caps the percentage of a company’s shares an investor can be treated as owning or controlling for voting, regulatory or tax purposes. It matters to investors because it can restrict how many shares a person or group can buy or vote, affect takeover chances, and influence share liquidity and value — like a speed limit that prevents any single driver from taking over the whole road.

beneficially owned financial

"The aggregate amount of shares of Common Stock that may be deemed beneficially owned by the Reporting Persons is comprised of"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

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

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FAQ

What stake in Atara Biotherapeutics (ATRA) does Redmile currently report?

Redmile and related entities report beneficial ownership of 950,994 shares of Atara Biotherapeutics common stock, representing 9.9% of the outstanding class, based on shares outstanding plus shares issued and issuable under certain warrants.

How is Redmile’s 950,994-share position in ATRA structured?

The reported 950,994 shares include 636,852 shares of common stock held by Redmile-managed funds and 314,142 shares issuable upon exercise of pre-funded warrants, limited by a 9.99% Beneficial Ownership Limitation.

What warrant exercises involving ATRA shares did Redmile complete in July 2026?

On July 16, 2026, Redmile exercised certain pre-funded warrants via a cashless exercise, resulting in 174,247 shares issued to RBI II and 20,904 shares issued to Redmile Strategic Long Only, with 60 total shares withheld to pay the exercise price.

How many Atara (ATRA) shares are underlying Redmile’s remaining warrants?

Redmile-managed funds hold warrants exercisable into 3,217,632 shares of Atara common stock, including 1,879,855 shares underlying remaining RBI II warrants and 806,670 shares underlying remaining Redmile Strategic Long Only warrants, all subject to the Beneficial Ownership Limitation.

When did Redmile Strategic Long Only Trading Sub, Ltd. fall below 5% ownership of ATRA?

Redmile Strategic Long Only Trading Sub, Ltd. is reported to have ceased to be a 5% beneficial owner of Atara common stock on July 22, 2026, solely as a result of the pre-funded warrant exercises described.

What share count did Redmile use to calculate its 9.9% ownership in ATRA?

The 9.9% ownership is based on 9,010,172 shares outstanding as of May 8, 2026, plus 195,151 shares issued upon warrant exercises, plus 314,142 shares issuable under warrants within the Beneficial Ownership Limitation.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 3)

Atara Biotherapeutics, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

046513206

(CUSIP Number)

Redmile Group, LLC
900 Larkspur Landing Circle, Suite 270,
Larkspur, CA, 94939
(415) 489-9980

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

07/22/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Group, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 950,994.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 950,994.00

11

Aggregate amount beneficially owned by each reporting person

950,994.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

IA, OO

Comment for Type of Reporting Person:

(1) The source of funds was working capital of certain private investment funds managed by Redmile Group, LLC (the "Redmile Funds"), including Redmile Biopharma Investments II, L.P. ("RBI II") and Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only"). (2) The information in Item 5(a) relating to the shares of common stock, par value $0.0001 per share, of the Issuer (the "Common Stock") that are or may be deemed beneficially owned by Redmile Group, LLC ("Redmile") and the calculation of the percent of such class of securities is incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Green Jeremy

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED KINGDOM

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 950,994.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 950,994.00

11

Aggregate amount beneficially owned by each reporting person

950,994.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

IN, HC

Comment for Type of Reporting Person:

(1) The source of funds was working capital of the Redmile Funds, including RBI II and Redmile Long Only. (2) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Jeremy Green and the calculation of the percent of such class of securities is incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Biopharma Investments II, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 631,020.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 631,020.00

11

Aggregate amount beneficially owned by each reporting person

631,020.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

6.6 %

14

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person:

(1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by RBI II and the calculation of the percent of such class of securities is incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Strategic Long Only Trading Sub, Ltd.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 401,901.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 401,901.00

11

Aggregate amount beneficially owned by each reporting person

401,901.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.2 %

14

Type of Reporting Person (See Instructions)

CO

Comment for Type of Reporting Person:

(1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Redmile Long Only and the calculation of the percent of such class of securities is incorporated by reference herein.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.0001 per share
(b)	Name of Issuer: Atara Biotherapeutics, Inc.
(c)	Address of Issuer's Principal Executive Offices: 1280 Rancho Conejo Blvd, Thousand Oaks, CALIFORNIA , 91320.
Item 2.	Identity and Background
(a)	This Amendment No. 3 to Schedule 13D (this "Amendment") amends and supplements the Schedule 13D filed with the SEC on May 23, 2025, which was previously amended and supplemented by that Amendment No. 1 to Schedule 13D filed with the SEC on November 14, 2025 and that Amendment No. 2 to Schedule 13D filed with the SEC on May 14, 2026 (collectively, the "Prior Schedule 13D"). This Amendment reports the exercise of certain pre-funded warrants to purchase Common Stock (the "Warrants") by Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only") and Redmile Biopharma investments II, L.P. ("RBI II" and collectively with Redmile Long Only, Redmile Group, LLC and Jeremy Green, the "Reporting Persons") described in Item 5(a) below and the resulting change in the beneficial ownership of Redmile Long Only following such exercise. Capitalized terms used but not defined in this Amendment shall have the meanings set forth in the Prior Schedule 13D. Except as specifically amended by this Amendment, the Prior Schedule 13D is unchanged.
Item 3.	Source and Amount of Funds or Other Consideration
	On July 16, 2026, Redmile Group, LLC ("Redmile") exercised certain Warrants held by RBI II and Redmile Long Only through a "cashless exercise" to acquire the Issuer's Common Stock. The transactions resulted in the Issuer (i) withholding 53 shares of Common Stock from RBI II and 7 shares of Common Stock from Redmile Long Only to pay the exercise price under the terms of the Warrants and (ii) issuing the remaining 174,247 shares of Common Stock to RBI II and 20,904 shares of Common Stock to Redmile Long Only.
Item 5.	Interest in Securities of the Issuer
(a)	Item 5(a) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: The aggregate amount of shares of Common Stock that may be deemed beneficially owned by the Reporting Persons is comprised of (i) 636,852 shares of Common Stock held by certain investment vehicles for which Redmile is the investment manager (the "Redmile Funds"), including the 316,878 shares of Common Stock directly held by RBI II and the 87,759 shares of Common Stock directly held by Redmile Long Only, and (ii) 314,142 shares of Common Stock issuable to the Redmile Funds, including RBI II and Redmile Long Only, upon exercise of certain Warrants, which is the maximum number of shares of Common Stock that could be issued upon exercise of the Warrants under the 9.99% beneficial ownership limitation (the "Beneficial Ownership Limitation"). The Redmile Funds hold Warrants that may be exercised into 3,217,632 shares of Common Stock issuable upon exercise of the Warrants, including the 1,879,855 shares of Common Stock issuable upon exercise of the remaining Warrants directly held by RBI II, and the 806,670 shares of Common Stock issuable upon exercise of the remaining Warrants directly held by Redmile Long Only, each of which is subject to the Beneficial Ownership Limitation. All of the reported securities are directly owned by certain Redmile Funds, including RBI II and Redmile Long Only. Redmile may be deemed to beneficially own these securities in its capacity as their investment manager with discretion to vote and dispose of the securities held by the Redmile Funds. Mr. Green also may be deemed to beneficially own these securities as the principal of Redmile. Redmile and Mr. Green each disclaim beneficial ownership of these securities, except to the extent of its or his pecuniary interest in such securities, if any. Percentage based on the sum of: (i) 9,010,172 shares of Common Stock outstanding as of May 8, 2026, as reported by the Issuer in its Form 10-Q for the quarterly period ended March 31, 2026 filed with the Securities and Exchange Commission on May 12, 2026, plus (ii) 195,151 shares of Common Stock issued to RBI II and Redmile Long Only upon exercise of certain Warrants, plus (iii) 314,142 shares of Common Stock issuable upon exercise of certain Warrants directly held by the Redmile Funds, which due to the Beneficial Ownership Limitation is the maximum number of shares that could be issued upon exercise of those Warrants.
(b)	Item 5(b) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: Redmile: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 Jeremy C. Green: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 RBI II: (1) Sole Voting Power: 0 (2) Shared Voting Power: 631,020 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 631,020 Redmile Long Only: (1) Sole Voting Power: 0 (2) Shared Voting Power: 401,901 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 401,901
(c)	See the response to Item 3. Except as disclosed in Item 3, no reportable transactions were effected by any Reporting Persons during the past sixty days.
(e)	Redmile Long Only ceased to be a 5% beneficial owner on July 22, 2026 solely as a result of the exercise of the pre-funded warrants described in Item 3 above.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Redmile Group, LLC

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member
Date:	07/24/2026

Green Jeremy

Signature:	/s/ Jeremy C. Green
Name/Title:	Jeremy C. Green
Date:	07/24/2026

Redmile Biopharma Investments II, L.P.

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member of Redmile Biopharma Investments II (GP), LLC, general partner of Redmile Biopharma Investments II, L.P.
Date:	07/24/2026

Redmile Strategic Long Only Trading Sub, Ltd.

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member of Redmile Group, LLC, investment manager of Redmile Strategic Long Only Trading Sub, Ltd.
Date:	07/24/2026