Anthropic Traces Six Weeks of Claude Code Quality Complaints to Three Overlapping Product Changes

Anthropic published a postmortem tracing six weeks of Claude Code quality complaints to three overlapping product-layer changes: a reasoning effort downgrade, a caching bug that progressively erased the model's own thinking, and a system prompt verbosity limit that caused a 3% quality drop. The API and model weights were unaffected. All issues were resolved April 20.

By Steef-Jan Wiggers