Interacting with /v1/messages requires more than just a valid API key. Developers must track specific HTTP status codes to build resilient production loops. A 429 (Rate Limit) error indicates you have exceeded your Tier's capacity; you should implement Exponential Backoff. However, a 529 (Overloaded) is a server-side capacity spike on Anthropic's end—retrying too quickly here can exacerbate the issue.
Every request MUST include the anthropic-version header (currently 2023-06-01). This versioning system ensures that even if Anthropic updates their default model behavior or output format, your integration remains stable. Failing to provide this header results in an immediate 400 error.
| Code | Meaning | Strategy |
|---|---|---|
| 400 | Bad Request | Check JSON syntax/Roles |
| 401 | Authentication Error | Verify API Key |
| 429 | Rate Limited | Wait and retry (Exponential) |
| 529 | Overloaded | Switch regions/Wait |
You've been handed a fresh Anthropic API key. Configure your shell, then hit /v1/messages directly with curl — exactly like you would in production.