Anthropic details three bugs that degraded Claude responses

Anthropic published a post-mortem on three infrastructure bugs from August–September 2025 that caused garbled code and stray Thai or Chinese characters in English answers. At the worst hour on August 31, 16% of Sonnet 4 requests were affected, and about 30% of Claude Code users got at least one degraded response.

• At peak on August 31, 16% of Sonnet 4 requests hit 1M-context servers
• About 30% of Claude Code users received at least one degraded response
• On Bedrock misrouting peaked at 0.18% of requests, on Vertex AI below 0.0004%
• Internal evaluations missed the degradation; fixes fully rolled out by September 18