Claude Code Postmortem: Three Bugs Caused Quality Degradation, Now Fixed

Anthropic has published a postmortem explaining three separate issues that caused Claude Code quality degradation for some users over the past month. As of April 20 (v2.1.116), all three have been resolved. The API was not affected.

Issue 1: Default reasoning effort lowered (March 4 – April 7)

On March 4, Claude Code's default reasoning effort was changed from high to medium to reduce long latencies that made the UI appear frozen. This impacted Sonnet 4.6 and Opus 4.6. After user complaints about reduced intelligence, the change was reverted on April 7. Opus 4.7 now defaults to xhigh effort; other models default to high.

Issue 2: Caching bug dropped prior reasoning (March 26 – April 10)

On March 26, a change was shipped to clear older thinking from sessions idle over an hour. A bug caused this to happen every turn instead of once, making Claude seem forgetful and repetitive. Fixed on April 10. Affected Sonnet 4.6 and Opus 4.6.

Issue 3: Verbosity prompt hurt coding quality (April 16 – April 20)

On April 16, a system prompt instruction to reduce verbosity was added. In combination with other prompt changes, it degraded coding quality. Reverted on April 20. Impacted Sonnet 4.6, Opus 4.6, and Opus 4.7.

What they're doing differently

Anthropic is resetting usage limits for all subscribers as of April 23. They acknowledge that internal evals initially failed to reproduce these issues, and are improving monitoring and testing to catch such regressions earlier.