Canonical event

Anthropic publishes a Claude Code quality regression postmortem covering three product-harness changes

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.