A postmortem of three recent issues
Anthropic traced degraded Claude answers in August 2025 to three overlapping infrastructure bugs, one misrouting up to 16% of Sonnet 4 requests.
There were three bugs. (1) Context-window routing sent Sonnet 4 requests to 1M-context servers (0.8% of requests from 2025-08-05, 16% at the worst hour on 2025-08-31). (2) A TPU-server misconfiguration corrupted token generation from 2025-08-25. (3) An approximate top-k XLA:TPU compiler miscompilation. Fixes reached Bedrock by 2025-09-18.
- Date
- Wednesday, 17 September 2025
- Lab
- Anthropic
- Kind
- infra
- Access
- closed API
Anthropic says it serves Claude on AWS Trainium, NVIDIA GPUs and Google TPUs, so each platform needs separate validation. About 30% of Claude Code users hit at least one misrouted message in the period.
Sources
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