Summary

When the Anthropic API returns HTTP 529 (overloaded), OpenClaw fails to trigger model fallback and becomes completely unresponsive — even when working fallback models are configured.

Root Cause

resolveFailoverReasonFromError in src/agents/failover-error.ts handles 402, 429, 401/403, 408, 503, 400 — but not 529.

When 529 is returned:

1. coerceToFailoverError receives an error with no recognized status → returns null
2. model-fallback.ts sees !isFailoverError(normalized) → throw err immediately
3. Fallback loop is skipped entirely
4. OpenClaw becomes unresponsive until the primary model recovers

Fix

Add 529 to resolveFailoverReasonFromError:

// src/agents/failover-error.ts
if (status === 529) {
  return "timeout"; // Anthropic non-standard "overloaded" status
}

Notes

• HTTP 529 is Anthropic's non-standard status code for API overload
• This is particularly impactful for users routing through proxy providers where 529s are more frequent
• The fix is one line and fully backward compatible

Reproducibility

Any setup where the primary Anthropic provider returns 529 (overloaded) while fallback providers are healthy and configured.