{"filing":{"accession_number":"0001193125-26-377485","cik":"0002022626","ticker":"UPB","company_name":"Upstream Bio, Inc.","form":"8-K","filing_date":"2026-09-01","report_date":"2026-09-01","primary_document":"upb-20260901.htm","primary_document_url":"https://www.sec.gov/Archives/edgar/data/2022626/000119312526377485/upb-20260901.htm"},"events":[{"id":30773,"run_id":28211,"accession_number":"0001193125-26-377485","anchor_item_number":"8.01","event_type":"operational_other","event_domain":"operational","is_material":true,"confidence":0.85,"summary":"Upstream Bio announced pivotal Phase 3 development plans for verekitug in severe asthma and CRSwNP following FDA End-of-Phase 2 meetings, including a 400mg every 12-week dosing regimen, trial design with approximately 1,500 patients across both indications, and planned Q1 2027 initiation with potential BLA submission and launch as early as 2030. This represents a material clinical development milestone with significant implications for the drug's regulatory pathway and commercial potential.","company_name":"Upstream Bio, Inc.","ticker":"UPB","filing_date":"2026-09-01","form":"8-K","submitted_at":null,"items":[{"id":33479,"accession_number":"0001193125-26-377485","item_number":"7.01","item_title":null,"event_type":"operational_other","event_domain":"operational","is_material":true,"confidence":0.75,"reasoning":"Upstream Bio announced pivotal Phase 3 development plans for verekitug following FDA End-of-Phase 2 meetings, including dosing strategy (400mg every 12 weeks), trial design (one placebo-controlled trial per indication), and initiation timeline (Q1 2027). This is a material clinical development milestone for a clinical-stage biotech company with significant implications for the drug's regulatory pathway and commercial potential, but does not fit the specific categories of earnings release, M\u0026A, impairment, or other named event types. It is clearly operational/strategic in nature.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-09-01T11:06:41.495497+00:00","company_name":"","ticker":null,"filing_date":""},{"id":33480,"accession_number":"0001193125-26-377485","item_number":"8.01","item_title":null,"event_type":"operational_other","event_domain":"operational","is_material":true,"confidence":0.85,"reasoning":"Upstream Bio announced pivotal Phase 3 development plans for verekitug in severe asthma and CRSwNP, including dosing regimen (400mg every 12 weeks), trial design (approximately 1,500 patients across both indications), and primary endpoints. The company remains on track to initiate Phase 3 trials in Q1 2027 with potential BLA submission and launch as early as 2030. This is a material operational/clinical development milestone for a clinical-stage biotech company, representing a significant advancement in the drug development pipeline following productive FDA End-of-Phase 2 meetings. While not fitting the specific categories of earnings, M\u0026A, litigation, or other named events, this clinical development announcement is clearly material to investors' assessment of the company's progress and commercial prospects.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-09-01T11:06:41.495497+00:00","company_name":"","ticker":null,"filing_date":""}]}],"classifications":[{"id":33479,"accession_number":"0001193125-26-377485","item_number":"7.01","item_title":null,"event_type":"operational_other","event_domain":"operational","is_material":true,"confidence":0.75,"reasoning":"Upstream Bio announced pivotal Phase 3 development plans for verekitug following FDA End-of-Phase 2 meetings, including dosing strategy (400mg every 12 weeks), trial design (one placebo-controlled trial per indication), and initiation timeline (Q1 2027). This is a material clinical development milestone for a clinical-stage biotech company with significant implications for the drug's regulatory pathway and commercial potential, but does not fit the specific categories of earnings release, M\u0026A, impairment, or other named event types. It is clearly operational/strategic in nature.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-09-01T11:06:41.495497+00:00","company_name":"Upstream Bio, Inc.","ticker":"UPB","filing_date":"2026-09-01"},{"id":33480,"accession_number":"0001193125-26-377485","item_number":"8.01","item_title":null,"event_type":"operational_other","event_domain":"operational","is_material":true,"confidence":0.85,"reasoning":"Upstream Bio announced pivotal Phase 3 development plans for verekitug in severe asthma and CRSwNP, including dosing regimen (400mg every 12 weeks), trial design (approximately 1,500 patients across both indications), and primary endpoints. The company remains on track to initiate Phase 3 trials in Q1 2027 with potential BLA submission and launch as early as 2030. This is a material operational/clinical development milestone for a clinical-stage biotech company, representing a significant advancement in the drug development pipeline following productive FDA End-of-Phase 2 meetings. While not fitting the specific categories of earnings, M\u0026A, litigation, or other named events, this clinical development announcement is clearly material to investors' assessment of the company's progress and commercial prospects.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-09-01T11:06:41.495497+00:00","company_name":"Upstream Bio, Inc.","ticker":"UPB","filing_date":"2026-09-01"}]}