{"event":{"id":"evt-hist-20260423-claudecode-quality","dedupe_key":"published_engineering_incident_postmortem:2026-04-23:anthropic-publishes-a-claude-code-quality-regression-postmortem-covering-three-product-harness-changes","event_type":"published_engineering_incident_postmortem","title":"Anthropic publishes a Claude Code quality regression postmortem covering three product-harness changes","summary":"Anthropic's April 23, 2026 engineering report attributes some Claude Code, Agent SDK and Cowork quality problems to changes on March 4, March 26 and April 16: lower default reasoning effort, a stale-session context retention bug, and a verbosity prompt that degraded coding. Anthropic reports reversing/fixing these issues by April 20. It explicitly says its API/inference models were not impacted. These are provider-reported root-cause and remediation findings, not an independently replicated incident audit.","occurred_at":"2026-04-23T00:00:00.000Z","published_at":"2026-04-23T00:00:00.000Z","observed_at":"2026-10-17T15:26:35.000Z","reconstructed_at":"2026-10-17T15:26:35.000Z","ingest_type":"historical_backfill","locations":null,"status":"verified","confidence":0.96,"metadata":{"external_postcutoff_id":"2026-04-23-claude-code-quality-postmortem","milestone":"primary_source_postmortem_publication","evidence_only":1,"new_relation_onset":0,"date_precision":"day","underlying_incident_and_remediation_dates":"2026-03-04;2026-03-26;2026-04-16;2026-04-20","epistemic_scope":"first_party_root_cause_claim","canonical_inventory_exhaustive":0},"created_at":"2026-10-17T15:54:55.842Z","updated_at":"2026-10-17T15:54:55.842Z"},"artifacts":[{"id":"art-hist-20260423-claudecode-quality","dedupe_key":"052a0155b95d47620d07eba89a677ee612598f08f88c61959ff1d54a438e4db6","canonical_url":"https://www.anthropic.com/engineering/april-23-postmortem","evidence_locator":"","artifact_type":"first_party_technical_postmortem","title":"An update on recent Claude Code quality reports","summary":"","creator_entities":[],"released_at":"2026-04-23T00:00:00.000Z","content_hash":null,"metadata":[],"created_at":"2026-10-17T15:54:55.841Z","updated_at":"2026-10-17T15:54:55.841Z","relation":"documented_by"}],"signals":[]}