{"schema_version":"secwatch.filing_event.v1","accession":"0000950170-25-112898","form_type":"8-K","ticker":"ATRA","cik":"0001604464","company_name":"Atara Biotherapeutics, Inc.","filed_at":"2025-09-04T23:59:59+00:00","discovered_at":"2026-05-14T18:02:44.471790+00:00","generated_at":"2026-05-17T08:18:05.762473+00:00","sec_items":["5.02"],"event_type":"leadership","sentiment":"neutral","materiality_score":0.4,"calibrated_materiality_score":0.4,"confidence":"high","headline":"Three directors resign from Atara Biotherapeutics board; Ciongoli named Chair","bullets":["Directors Ameet Mallik, Pascal Touchon, and Maria Grazia Roncarolo resigned voluntarily effective Sept 2, 2025.","Board size reduced from 10 to 7 directors as of the same date.","Gregory A. Ciongoli appointed as Chair to succeed Pascal Touchon."],"urls":{"canonical":"https://secwatch.observer/filing/0000950170-25-112898","json":"https://secwatch.observer/filing/0000950170-25-112898.json","markdown":"https://secwatch.observer/filing/0000950170-25-112898.md","text":"https://secwatch.observer/filing/0000950170-25-112898.txt","edgar_index":"https://www.sec.gov/Archives/edgar/data/1604464/000095017025112898/0000950170-25-112898-index.htm","edgar_primary_document":"https://www.sec.gov/Archives/edgar/data/1604464/000095017025112898/atra-20250902.htm"},"model":{"generated_by":"deepseek-v4-flash:cloud@v2","generated_at":"2026-05-17T08:18:05.762473+00:00"},"review":{"review_status":"machine_generated","human_reviewed":false,"corrected":false,"correction_note":null,"correction_timestamp":null,"superseded_by":null,"related_filings":[]},"source_grounded_claims":[],"license":"Source filings: public domain (SEC EDGAR). Summaries (headline + bullets): CC-BY-4.0; attribute https://secwatch.observer"}