$ATRA

$8.30 -$0.05 (0.6%) Close

$ATRA Overview Financial Statements SEC Filings Executives News Red Flags Capital Raising Ownership Insider Transactions Congressional Trades

Ownership

13F as of Q2 2026 · 10.0M shares outstanding

Who owns ATRA?

By type of holder

Institutions 44.5% Insiders 55.5% Everyone else 0.0%

Concentration Top 10 holders own 117.6%

EcoR1 Capital, LLC 15.5% · Adiumentum Capital Fund I LP 13.7%

Institutional ownership

44.5%

+19.0 pts vs last qtr

Institutional holders

+3 vs last qtr

Net shares bought

+1.9M

by institutions in Q2 2026

New / sold out

4 / 1

positions opened vs closed

How is ownership changing?

Institutions, last 8 quarters

Biggest buyers in Q2 2026

EcoR1 Capital, LLC +1.5M
Point72 Asset Management, L.P. +493.5K

Biggest sellers in Q2 2026

Acadian Asset Management LLC −92.1K
Mackenzie Financial Corp −80.4K

Who is planning to sell?

Notices of proposed sale, last 12 months

$3.6M

8 notices from 3 people

Shares covered

373.3K

3.72% of the company

Arranged in advance

of the value is under a 10b5-1 plan

Under a 10b5-1 plan No plan

Largest proposed sellers

Panacea Innovation Ltd 10% stockholder $3.4M
Nguyen AnhCo Director $127K

Every notice on Red Flags →

A Form 144 is notice of a planned sale, not the sale itself. What insiders actually sold is on Insider Transactions.

Is your stake being diluted?

Diluted share count, FY2020–FY2025

+312.6%

+32.77% a year

Each share's claim on the business

−75.8%

shrank without buying or selling a share

Spent on buybacks vs paid in stock

— vs $241M

over 6 fiscal years

Diluted shares, split-adjusted

Buybacks Stock-based comp

How patient are the owners?

Institutional shares by how long they've been held

5+ years22% 3–5 years1% 1–3 years41% Under 1 year36%

Quarterly turnover

47.9%

of institutional shares changed hands

Top 10 managers, median time held

5 years

Super Investors

Investment managers reporting ATRA on Form 13F

Holder	Shares	% of company	Change vs last qtr	Held since	% of their book
EC EcoR1 Capital, LLC	1.6M	15.46%	+1.5M (+1458.3%)	2023	0.9%
Shares held by quarter Peak holding1.6M (Q2'26) Change over 8 quarters+1.1M Share of the company15.460% EcoR1 Capital, LLC's full portfolio →
AC Adage Capital Partners GP, L.L.C.	850.0K	8.47%	+150.0K (+21.4%)	Q1 '26	0.0%
Shares held by quarter Peak holding850.0K (Q2'26) Change over 8 quarters+850.0K Share of the company8.470% Adage Capital Partners GP, L.L.C.'s full portfolio →

EcoR1 Capital, LLC

1.6M

% of company

15.46%

Change vs last qtr

+1.5M (+1458.3%)

Held since

2023

Adage Capital Partners GP, L.L.C.

850.0K

% of company

8.47%

Change vs last qtr

+150.0K (+21.4%)

Held since

Q1 '26

24 more super investors behind a free account

See every manager holding Atara Biotherapeutics, Inc., how their position has changed, and how long they've held it.

Institutional Funds

Mutual funds and ETFs reporting ATRA on Form N-PORT; together they hold 3.8% of the company

Fund	Position value	Shares	% of company	% of the fund	As of
VT Vanguard Total Stock Market Index Fund Vanguard Index Funds	$1.82M	158.6K	1.58%	0.00%	June 30, 2026
VE Vanguard Extended Market Index Fund Vanguard Index Funds	$950K	82.8K	0.82%	0.00%	June 30, 2026

Vanguard Total Stock Market Index Fund

Vanguard Index Funds

Position value

$1.82M

% of company

1.58%

% of the fund

0.00%

As of

June 30, 2026

Vanguard Extended Market Index Fund

Vanguard Index Funds

Position value

$950K

% of company

0.82%

% of the fund

0.00%

As of

June 30, 2026

17 more funds behind a free account

See every fund holding Atara Biotherapeutics, Inc. and how much of the fund the position is.

Insiders and 5%+ holders

From Forms 3/4/5 and Schedules 13D/G

Holder	Shares	% of company	Change vs last qtr	8 quarters	Held since	% of their book
AC Adiumentum Capital Fund I LP 5%+ holder 13D · 20.0%	1.4M	13.65%	—	—	—	—
This holder reports through Schedule 13D/G, not a quarterly 13F. Share of the company13.650% Disclosed stake13D · 20.0% View the 13D/G filing →
AC Adiumentum Capital Fund I GP LLC 5%+ holder 13D · 20.0%	1.4M	13.65%	—	—	—	—
This holder reports through Schedule 13D/G, not a quarterly 13F. Share of the company13.650% Disclosed stake13D · 20.0% View the 13D/G filing →

Adiumentum Capital Fund I LP

5%+ holder13D · 20.0%

1.4M

% of company

13.65%

Change vs last qtr

—

Held since

—

Adiumentum Capital Fund I GP LLC

5%+ holder13D · 20.0%

1.4M

% of company

13.65%

Change vs last qtr

—

Held since

—

19 more holders behind a free account

See every insider and 5%+ holder of Atara Biotherapeutics, Inc..

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