What a 529 means and how to retry

Retry with backoff

A 529 overloaded_error is specific to the Anthropic-compatible /v1/messages endpoint when upstream capacity is saturated; OpenAI-compatible endpoints return 503 instead. Timeout- and overload-class errors are not billed. Retry with exponential backoff and jitter rather than an immediate loop; the status page shows whether an incident or a maintenance window explains the errors you see.