Errors

HTTP errors

The API follows a predictable HTTP error code format:

• 400 - invalid_request_error: There was an issue with the format or content of your request. This error type may also be used for other 4XX status codes not listed in this section.

• 401 - authentication_error: There's an issue with your API key. On Claude Platform on AWS, this can also indicate a problem with your AWS credentials or SigV4 signature.

• 402 - billing_error: There's an issue with your billing or payment information. Check your payment details in the Claude Console, or in AWS Marketplace if you're using Claude Platform on AWS.

• 403 - permission_error: Your API key does not have permission to use the specified resource.

• 404 - not_found_error: The requested resource was not found.

• 413 - request_too_large: Request exceeds the maximum allowed number of bytes. See Request size limits for per-endpoint maximums.

• 429 - rate_limit_error: Your account has hit a rate limit.

• 500 - api_error: An unexpected error has occurred internal to Anthropic's systems.

• 504 - timeout_error: The request timed out while processing. Consider using streaming for long-running requests.

• 529 - overloaded_error: The API is temporarily overloaded.

  529 errors can occur when APIs experience high traffic across all users.

  In rare cases, if your organization has a sharp increase in usage, you might see 429 errors because of acceleration limits on the API. To avoid hitting acceleration limits, ramp up your traffic gradually and maintain consistent usage patterns.

When receiving a streaming response over SSE, it's possible that an error can occur after returning a 200 response, in which case error handling wouldn't follow these standard mechanisms.

Request size limits

The API enforces request size limits to ensure optimal performance:

If you exceed these limits, you'll receive a 413 request_too_large error. On the direct Claude API, this error is returned from Cloudflare before the request reaches the API servers.

Error shapes

Errors are always returned as JSON, with a top-level error object that always includes a type and message value. The response also includes a request_id field for easier tracking and debugging. For example:

{
  "type": "error",
  "error": {
    "type": "not_found_error",
    "message": "The requested resource could not be found."
  },
  "request_id": "req_011CSHoEeqs5C35K2UUqR7Fy"
}

In accordance with the versioning policy, the values within these objects may expand, and it is possible that the type values will grow over time.

Request ID

Every API response includes a unique request-id header. This header contains a value such as req_018EeWyXxfu5pfWkrYcMdjWG. When contacting support about a specific request, include this ID to help quickly resolve your issue.

On Claude Platform on AWS, responses include two request IDs: the AWS request ID (x-amzn-requestid, primary, indexed in CloudTrail) and the Anthropic request ID (request-id, secondary). Use the AWS request ID for CloudTrail lookups and the Anthropic request ID for Anthropic support tickets.

The official SDKs provide the Anthropic request ID as a property on top-level response objects, containing the value of the request-id header. On Claude Platform on AWS, use the raw-response accessor to also read the AWS request ID from the HTTP headers:

client = anthropic.Anthropic()

message = client.messages.create(
    model="claude-opus-4-7",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello, Claude"}],
)
print(f"Request ID: {message._request_id}")

For Claude Platform on AWS request-ID examples in other languages, see Request IDs.

Long requests

Avoid setting a large max_tokens value without using the streaming Messages API or Message Batches API:

• Some networks may drop idle connections after a variable period of time, which can cause the request to fail or timeout without receiving a response from Anthropic.
• Networks differ in reliability; the Message Batches API can help you manage the risk of network issues by allowing you to poll for results rather than requiring an uninterrupted network connection.

If you are building a direct API integration, you should be aware that setting a TCP socket keep-alive can reduce the impact of idle connection timeouts on some networks.

The SDKs validate that your non-streaming Messages API requests are not expected to exceed a 10 minute timeout and also will set a socket option for TCP keep-alive.

If you don't need to process events incrementally, use .stream() with .get_final_message() (Python) or .finalMessage() (TypeScript) to get the complete Message object without writing event-handling code:

with client.messages.stream(
    max_tokens=128000,
    messages=[{"role": "user", "content": "Write a detailed analysis..."}],
    model="claude-opus-4-7",
) as stream:
    message = stream.get_final_message()
print(message.content)

See Streaming Messages for more details.

Common validation errors

Prefill not supported

Claude Mythos Preview, Claude Opus 4.7, Claude Opus 4.6, and Claude Sonnet 4.6 do not support prefilling assistant messages. Sending a request with a prefilled last assistant message to any of these models returns a 400 invalid_request_error:

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "Prefilling assistant messages is not supported for this model."
  }
}

Use structured outputs, system prompt instructions, or output_config.format instead.

Outbound web identity federation disabled (Claude Platform on AWS)

If every request to Claude Platform on AWS returns "Outbound web identity federation is disabled for your account", run aws iam enable-outbound-web-identity-federation once per AWS account. See Enable outbound web identity federation for details.