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A Claude API failure is easiest to fix when you start with two values from the response: the HTTP status and Anthropic’s request_id. The status identifies the broad cause—bad input, authentication, billing, permissions, a size limit, throttling, overload, or a timeout. Correct client or account problems first; retry only transient failures with bounded exponential backoff and jitter.
This guide explains what each common Claude error means, how to verify the diagnosis, and what to change in direct Anthropic API integrations and Amazon Bedrock deployments.
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Start with the response, not the retry loop
Log the complete diagnostic context before changing code. Keep secrets out of logs, but record the following fields:
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- HTTP status code.
- Anthropic error
typeand human-readablemessage. request_id(or the provider’s equivalent request identifier).- Model ID, API endpoint, deployment or region, and timestamp in UTC.
- Whether the request was streamed, batched, sent through Files, or routed through Amazon Bedrock.
- Relevant response headers, including
retry-afterwhen present.
A request ID lets Anthropic support correlate a failed call with server logs. It does not by itself make a request retryable. The status and error type determine the next action.
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Claude error statuses at a glance
| Status | Anthropic error family | Typical cause | Can a retry help? | Primary evidence or remedy |
|---|---|---|---|---|
| 400 | invalid_request_error |
Payload shape, parameter, model-rule, or prompt-format violation | No, until the request changes | Compare the payload with the selected model’s current requirements |
| 401 | Authentication error | Missing, invalid, revoked, or expired API key | No | Validate the key and authentication header |
| 402 | Billing error | Payment or account billing problem | No, until billing is corrected | Check billing status in the Console |
| 403 | Permission error | Organization or workspace is not allowed to use the resource | No | Confirm organization, workspace, and model permissions |
| 404 | Not found | Wrong endpoint path, model ID, or other resource identifier | No, unless the identifier is corrected | Verify the exact path and resource ID |
| 409 | Conflict | Concurrent or incompatible resource state | Only after the conflicting state is resolved | Read the conflict message and serialize or reconcile the operation |
| 413 | request_too_large |
Request exceeds a byte-size limit | No, without shrinking or splitting the request | Measure bytes and reduce, split, compress, or change the file workflow |
| 429 | rate_limit_error |
Request-rate limit, usage-tier spending cap, or Claude Code workspace spending limit | Sometimes | Inspect headers, Console usage, billing, and tier status |
| 500 | api_error |
Internal Anthropic API failure | Yes, with bounded backoff | Retry; escalate persistent failures with the request ID |
| 504 | timeout_error |
Processing exceeded the service timeout | Often | Stream long responses, trim unnecessary prompt content, and allow an adequate client timeout |
| 529 | overloaded_error |
Temporary API overload | Yes | Use exponential backoff, jitter, and a maximum attempt count |
Fixing a 429 rate-limit error
A 429 is not always a short-lived burst throttle. Anthropic documents three distinct causes: the organization can exceed a request-rate limit, the account can hit the monthly spending cap for its usage tier, or a Claude Code workspace can reach its spending limit. Those cases require different responses.
When it is temporary throttling
If the response supplies retry guidance, honor the stated delay. A worker pool should add random jitter so that all workers do not retry at the same instant. Reduce concurrency or queue work when the same limit is repeatedly reached. Keep the original request ID and the retry attempt in logs so you can see whether calls are eventually succeeding.
When it is a spending cap
A 429 caused by a usage-tier spending cap has no retry-after header and continues failing until access resumes. Waiting longer or adding more attempts cannot clear that condition. Open the Claude Console and check usage, billing, and the organization’s tier status. Raise or otherwise resolve the applicable cap, then test one request before releasing a large queue.
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- Do not treat every 429 as proof that the server is overloaded.
- Do not launch unlimited parallel retries; they increase pressure and can prolong throttling.
- Do not hide 429s behind a generic “network error” that prevents operators from seeing the spending-cap case.
Handling 529 overload, 500 API failures, and 504 timeouts
529: temporary overload
overloaded_error means the API is temporarily overloaded. Preserve the request ID, pause, and retry with exponential backoff plus jitter. Set a hard attempt or elapsed-time limit. If many clients share one queue, use a centralized rate limiter rather than allowing every process to retry independently.
500: internal API error
Anthropic recommends exponential-backoff retries for a 500 api_error. A continued sequence of 500 responses is a support case, not a reason to retry forever. Send support the request ID, UTC timestamps, model and endpoint, a sanitized reproducible request, and the number of attempts.
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504: processing timeout
A 504 indicates that processing did not finish within the service’s time window. Anthropic suggests Messages API streaming for long-running requests. Remove unnecessary prompt material and set the client-side timeout high enough to accommodate the server’s work; an overly short client timeout can make a healthy server response look like a failure to your application. Streaming changes how you consume the result, so make sure your code handles partial events and reconnect or replay policy deliberately.
Correcting 400 invalid-request errors
A 400 is a client request-validation failure. Retrying an identical payload will return the same result. Compare the serialized request—not just the object before middleware—with the current documentation for the exact model.
Assistant prefill and newer Claude models
Anthropic documents 400 responses for unsupported assistant-message prefilling on Claude 4.6 and later and on Claude Mythos Preview. Remove the assistant prefill, or use the model’s documented prompting pattern instead.
Thinking blocks and thinking settings
Modified or reordered thinking blocks can invalidate a request. Preserve the block structure returned by the API when a subsequent request is expected to include it; do not edit, reorder, or synthesize those blocks. Unsupported thinking settings also produce 400 responses, so compare the thinking mode and related fields with the selected model’s current schema.
Sampling parameters
Some newer models reject non-default temperature, top_p, or top_k. Remove those fields unless the model documentation explicitly permits the value you are sending. A shared SDK configuration that worked for an older model can therefore fail immediately after a model switch.
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A practical payload diff
- Capture the final JSON after templating, middleware, and SDK serialization.
- Record the model ID and API version used for that call.
- Compare required fields, message roles, content-block types, thinking configuration, and sampling parameters with the model’s current reference.
- Remove one suspect field at a time and replay a minimal request.
- Once the minimal call succeeds, add application fields back incrementally.
Fixing 413 request-too-large failures
Size limits are measured in bytes and can be reached before a model’s token-window limit. Anthropic’s direct API documentation lists these maximum request sizes:
| Direct API operation | Maximum request size | Typical response |
|---|---|---|
| Messages | 32 MB | Split or reduce the message payload |
| Token Counting | 32 MB | Send smaller chunks for counting |
| Batch | 256 MB | Partition the batch |
| Files | 500 MB | Use the Files workflow or divide the upload |
Measure the encoded HTTP body, not only the source-text length. Base64 images, JSON escaping, repeated context, and multipart boundaries add bytes. Reduce embedded image resolution, compress suitable documents, remove duplicated instructions, or split work into independent requests. If you split a document, include stable section identifiers so your application can reassemble results without asking the model to infer missing context.
Authentication, billing, permission, resource, and conflict errors
401 authentication
Confirm that the API key is present in the expected header, belongs to the intended organization, has not been revoked, and has not expired. Check environment selection in the process that actually makes the request; a local shell can contain a different key from the production worker. Never print the key while debugging.
402 billing
Resolve payment or billing configuration in the account that owns the request. A successful key check does not prove that the organization can incur additional usage.
403 permissions
Verify organization and workspace membership and whether that workspace is permitted to use the requested model, endpoint, or file resource. If your application switches workspaces, log the non-secret workspace identifier alongside the request.
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404 missing resource
Check the endpoint path, API version, model ID, and any file or batch identifier. Copy the identifier from the create response or current Console rather than relying on a stale configuration value.
409 conflict
A conflict means the server received a request that cannot be applied to the resource’s current concurrent state. Resolve the state mismatch—often by serializing updates, refreshing the resource, or using the latest version—before trying again. Blind retries can repeat the conflict.
When a Claude model suddenly stops working
Anthropic classifies models as active, legacy, deprecated, or retired. A retired model is unavailable, so requests using its ID fail rather than recover through retries. Audit model IDs in the Claude Console and replace retired or deprecated IDs with Anthropic’s listed replacements. Test the replacement’s request schema, output behavior, latency, and cost before its predecessor’s retirement date.
Anthropic’s lifecycle documentation cautions: “Deprecated models are likely to be less reliable than active models.” Treat a deprecation notice as migration work, not as a temporary outage.
Amazon Bedrock-specific failure modes
Bedrock adds routing and payload constraints beyond the direct Anthropic API.
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Inference-profile routing
Anthropic documents that newer Bedrock models may require an inference-profile ID or ARN instead of a base model ID. A direct-API model identifier copied into a Bedrock call can therefore fail even when the model name looks correct. Verify the model’s Bedrock invocation form for the selected region.
Bedrock’s payload ceiling
Bedrock limits request payloads to 20 MB. A document or image set can exceed that ceiling before Anthropic’s direct limits or the model’s token window become relevant. Measure the serialized Bedrock body and split or transform large inputs accordingly.
Global and regional endpoints
Global endpoints dynamically route requests for availability. Regional endpoints keep data in a chosen geography and carry a documented 10% pricing premium for Sonnet 4.5 and future models. Select the endpoint type deliberately: the routing and data-residency decision belongs in your deployment design, not in an emergency retry handler.
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Bedrock troubleshooting checklist
- Confirm the inference-profile ID or ARN required by the model.
- Check AWS region, account, IAM permissions, and endpoint type.
- Measure the request body against the 20 MB Bedrock limit.
- Determine whether a global or regional route was used when comparing logs.
- Only then investigate Anthropic status codes and model lifecycle state.
Implementing safe Claude retries
Retry policy should be status-aware and bounded. The following is a deliberately conservative pattern; choose limits that fit your workload and idempotency guarantees.
for attempt in range(1, max_attempts + 1):
response = call_claude(request)
if response.ok:
return response
status = response.status
error_type = response.error_type
request_id = response.request_id
log(status, error_type, request_id, attempt)
if status == 429 and response.retry_after is not None:
delay = response.retry_after + random_jitter()
elif status in (500, 504, 529):
delay = min(backoff_cap, initial_delay * (2 ** (attempt - 1)))
delay += random_jitter()
else:
raise NonRetryableClaudeError(response)
sleep(delay)
raise RetryLimitExceeded()Use idempotency protection where the operation can create a side effect outside the model response. For streamed calls, decide whether reconnecting can duplicate output and store enough request metadata to detect duplicates. A queue with a maximum age is safer than an infinite retry loop.
Quick Recap
A step-by-step incident workflow
- Classify the response. Record status, error type, message, request ID, model, endpoint, region, and timestamp.
- Separate permanent from transient causes. Treat 400, 401, 402, 403, 404, 409, and 413 as requiring a request, account, or configuration change. Treat 500, 504, and 529 as transient candidates. Treat 429 as ambiguous until headers and account usage are checked.
- Inspect 429 evidence. Read rate headers and Console usage, billing, and tier information. A spending-cap response without
retry-afteris not cleared by waiting. - Validate the 400 payload. Diff model-specific prefill, thinking blocks, thinking mode, and sampling parameters against current documentation.
- Measure bytes for 413. Check the serialized body and the applicable direct or Bedrock ceiling, then split or reduce it.
- Retry transient failures safely. Apply exponential backoff, jitter, a hard attempt limit, and concurrency control. Preserve request IDs across attempts.
- Check model lifecycle after model changes. A retired or deprecated ID requires migration, not retries.
- Handle Bedrock separately. Verify inference-profile routing, AWS region, endpoint type, and the 20 MB limit.
- Escalate with evidence. For persistent 500s or unexplained failures, provide support a request ID, timestamps, model and endpoint, sanitized payload, and a reproducible description.
Preventing repeat outages
- Keep model IDs and model-specific request settings in version-controlled configuration.
- Run a small compatibility test whenever a model ID changes.
- Alert separately on 429 spending caps, 429 throttles, 529 overloads, and 5xx errors.
- Track request bytes as well as input tokens.
- Make concurrency, queue age, retry count, and backoff visible in metrics.
- Stream workloads that can legitimately run for a long time, and test partial-response handling.
- Review model lifecycle notices before retirement dates.
- For Bedrock, document the inference profile, region, endpoint type, and data-residency choice for each deployment.
Choosing the right remedy
| Observed evidence | Change code? | Change billing or tier? | Change payload? | Change endpoint or model? |
|---|---|---|---|---|
| 429 with retry guidance and no spending-cap indication | Yes: honor delay, add jitter, limit concurrency | Not necessarily | No | No |
429 with no retry-after and a usage-tier cap |
No retry-loop change will solve it | Yes | No | No |
| 400 involving prefill, thinking, or sampling fields | Yes | No | Possibly | Possibly, if the model does not support the feature |
| 413 direct API or Bedrock | Yes: chunk or transform input | No | Yes | Possibly, for a suitable file workflow |
| 500, 504, or 529 | Yes: bounded retry and timeout/streaming handling | No | Often for 504 | No, unless the incident is model-specific |
| 404 after a model change | Configuration update | No | No | Yes: verify or migrate the model ID |
| Bedrock model invocation failure | Possibly | No | Check 20 MB limit | Verify inference profile, region, and endpoint type |
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