SEPTInvestingStart Free

ATRA 424B5: Secondary offering

Atara Biotherapeutics

Filed with the SEC on · accession 0001193125-26-219518

ATRA filed a 424B5 (prospectus (offering)) with the SEC on May 12, 2026. Atara Biotherapeutics filed a prospectus supplement to offer and sell up to $79,269,007 of common stock through TD Cowen under an existing at-the-market sales agreement, relying on a new SEC staff interpretation to continue the offering despite no longer meeting the $75 million public float… The stock moved +11.7% by the first close after the filing.

Summary of the filing

Atara Biotherapeutics filed a prospectus supplement to offer and sell up to $79,269,007 of common stock through TD Cowen under an existing at-the-market sales agreement, relying on a new SEC staff interpretation to continue the offering despite no longer meeting the $75 million public float requirement.

For details, click here →How to read a 424B5 →

Key details

remaining aggregate offering price of common stock$79.3M
IssuerAtara Biotherapeutics, Inc.
Sales agentTD Securities (USA) LLC

How ATRA stock reacted

Close before

$8.78

May 11, 2026

First close after

+11.73%

$9.81

5 trading days

+4.21%

$9.15

Since filing

-10.36%

$7.87

✦ Ask GOAX AI about this filing — what it means for ATRA, what changed since its last filings and what to watch next.

Try it free for 7 days

🔔 Want to stay updated on new SEC filings for ATRA?

Click here

Frequently asked questions

What did ATRA file with the SEC on May 12, 2026?

ATRA filed a 424B5 (Secondary offering). Atara Biotherapeutics filed a prospectus supplement to offer and sell up to $79,269,007 of common stock through TD Cowen under an existing at-the-market sales agreement, relying on a new SEC staff interpretation to continue the offering despite no longer meeting the $75 million public float requirement.

What does a secondary offering mean for ATRA stock?

New shares dilute existing holders and are often sold at a discount to the market price.

How do I read a 424B5?

The final terms of an offering of shares or bonds. Look at price, number of shares and the discount to the market price. Large offerings dilute existing shareholders.

Why are SEC filings important?

Public companies must tell the SEC about anything that can change their value — results, leadership changes, big deals, new shares, bankruptcy. Filings are the official source, often before the news. A 424B5 (prospectus (offering)): The final terms of an offering of shares or bonds.

How did ATRA stock react to this filing?

ATRA closed at $8.78 before the filing and $9.81 on May 12, 2026 (+11.73%). Five trading days later: $9.15 (+4.21%).

Other ATRA SEC filings

Get alerts when ATRA files with the SEC, plus live charts, key levels and news for 13,000+ stocks.

Try SEPT free for 7 days
ATRA overviewATRA analysisATRA newsLatest SEC filings