Atara Biotherapeutics, Inc. - Common Stock, par value $0.0001 per share (ATRA)

Q: What does CUSIP 046513206 represent in this 13F holders report?

CUSIP 046513206 is the security identifier for ATRA - Atara Biotherapeutics, Inc. - Common Stock, par value $0.0001 per share used to aggregate holder disclosures.

Q: How many institutions held ATRA - Atara Biotherapeutics, Inc. - Common Stock, par value $0.0001 per share in Q1 2026?

32 institutional investors reported ATRA - Atara Biotherapeutics, Inc. - Common Stock, par value $0.0001 per share for Q1 2026. Use the holders table for investor-level position and value details.

CUSIP: 046513206

Q1 2026 13F Holders as of 31 Mar 2026

Security type / class: Equity / Common Stock, par value $0.0001 per share
Total 13F shares: 2,564,230
Total 13F value: $12,126,238
Share change: +487,540
SEC-reported price per share: $4.73
Number of holders: 32
Value change: -$2,698,914
Number of buys: 12
Number of sells: 17
Shares outstanding: 9,606,000

Security key

046513206

Report period

Q1 2026

Institutions

Top holders

ATRA full security history Ownership snapshot Full 13F holder table Newer quarter: Q2 2026 Atara Biotherapeutics, Inc. SEC filings Atara Biotherapeutics, Inc. company facts

Broader feeds

Latest 13F filings Latest 13D/G filings Investors directory

Reporting periods

Holder history for CUSIP 046513206

Newer quarter: Q2 2026

Recent filing periods:

Q2 2026

Ownership snapshot

Top reported holders of ATRA - Atara Biotherapeutics, Inc. - Common Stock, par value $0.0001 per share (13F + 13D/G + 3/4/5)

Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.

Comparable stake leader

Adiumentum Capital Fund I LP

Disclosed value leader

Adiumentum Capital Fund I LP

Comparable rows

15/15

Latest evidence

31 Mar 2026

3/4/5 13D/G 13F Lead comparable stake: 20% 13D/G row: Adiumentum Capital Fund I LP Showing 1-6 of 15 holder rows.

Quick read

Adiumentum Capital Fund I LP leads the comparable SEC ownership view at 20%.

15 of 15 rows have a safely comparable ownership percentage. Use this as a filing-backed starting point, then open the detailed table for source links, reporting role, position value, share count, and filing date.

Open SEC evidence Opens Adiumentum Capital Fund I LP's linked filing trail.

Comparable ownership Top 5

Adiumentum Capital Fund I LP 20%

Panacea Innovation Ltd 20%

EcoR1 Capital, LLC 9.9%

Adage Capital Management, L.P. 8.6%

Pascal Touchon 0.81%

Ownership % is shown only when SEC disclosures are safely comparable across share classes.

Detailed SEC evidence table Showing 1-6 of 15 holder rows

Holder	Evidence	Ownership %	Position	12M Net Δ	As of
Adiumentum Capital Fund I LP	3/4/5 13D/G Director, Other*, 10%+ Owner 3/4/5 13D/G	20% from 13D/G	$10,487,308 1,586,588 shares mixed-class rows	—	16 May 2025
Panacea Innovation Ltd	13D/G Panacea Innovation Limited 13D/G	20%	— 1,632,345 shares	-$1,154,619	12 Jan 2026
EcoR1 Capital, LLC	13F 13D/G Company 13F 13D/G	9.9% from 13D/G	$10,368,880 573,183 shares	—	31 Dec 2025
Adage Capital Management, L.P.	13D/G 13D/G	8.6%	— 700,000 shares	$0	31 Mar 2026
Pascal Touchon	3/4/5 Director 3/4/5	0.81%	$589,339 77,955 shares	—	10 Jun 2025
Carol Giltner Gallagher	3/4/5 Director 3/4/5	0.34%	$249,570 33,012 shares	—	10 Jun 2025

How to read this table

Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.

13F holder rows

Institutional holders as of Q1 2026

Investor-level positions for this CUSIP, loaded as an interactive table.

Institutions

2,564,230

Rows available

Investor	Option	Weight %	Change %	SEC-reported value	* Price	Shares	Share Change	Activity	Report Period

^* SEC-reported price is the security price as of the portfolio date and can indicate the last known price at which the security was still held. The marker flags a reported price that did not pass the local price check.

Compare Q1 2026 vs Q1 2026 Across Filers

Q1 2026 holders

Holder diff

Investor	Q1 2026 Shares	Q1 2026 Shares	Share Diff	Share Chg %	Q1 2026 value	Q1 2026 value	Value change	Value Chg %

Trend: ostatnie 8 kwartałów (+ wybrane okresy porównania).

Quarterly Holders Trend

Quarterly Value Trend

Quarterly Shares Trend