Anthropic API / Anthropic API
Anthropic API Batch Processing undocumented 64-character custom_id limit
Fix Anthropic API batch processing error: custom_id character limit not documented, causing 400 BadRequestError Includes evidence for Anthropic API troubleshooting demand.
- Category
- Anthropic API
- Error signature
BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'requests.0.custom_id: String should have at most 64 characters'}}- Quick fix
- Compare the failing environment with a known working setup, then change one configuration value at a time.
- Updated
What this error means
BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'requests.0.custom_id: String should have at most 64 characters'}} is a Anthropic API failure pattern reported for developers trying to fix anthropic api batch processing error: custom_id character limit not documented, causing 400 badrequesterror. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.
Why this happens
GitHub issue anthropics/anthropic-sdk-python#984 (open since Jun 2025, updated May 2026): custom_id parameter for Message Batch Processing has an undocumented 64-character limit. Users hit BadRequestError 400 when exceeding it. The limit is not mentioned anywhere in the API documentation. Category mapping: Anthropic API (direct API error).
Common causes
- GitHub issue anthropics/anthropic-sdk-python#984 (open since Jun 2025, updated May 2026): custom_id parameter for Message Batch Processing has an undocumented 64-character limit. Users hit BadRequestError 400 when exceeding it. The limit is not mentioned anywhere in the API documentation. Category mapping: Anthropic API (direct API error).
Quick fixes
- Confirm the exact error signature matches
BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'requests.0.custom_id: String should have at most 64 characters'}}. - Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
- Compare the failing environment with a known working setup, then change one configuration value at a time.
Platform/tool-specific checks
- Verify the command, editor, extension, or API client that produced the error.
- Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
- Avoid deleting credentials, local model data, or project settings until the failing scope is clear.
Step-by-step troubleshooting
- Capture the exact error message and the command, editor action, or request that triggered it.
- Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
- Review the source evidence below and compare it with your environment.
- Apply one change at a time and rerun the smallest failing action.
- Keep the working fix documented for the team or deployment environment.
How to prevent it
- Keep provider/tool configuration documented.
- Record non-secret diagnostics such as tool version, provider name, model name, and command path.
- Add a lightweight check before CI or production workflows depend on the tool.
Sources checked
Evidence note: GitHub issue anthropics/anthropic-sdk-python#984 (open since Jun 2025, updated May 2026): custom_id parameter for Message Batch Processing has an undocumented 64-character limit. Users hit BadRequestError 400 when exceeding it. The limit is not mentioned anywhere in the API documentation. Category mapping: Anthropic API (direct API error).
Related errors
- Anthropic API
FAQ
What should I check first?
Start with the exact BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'requests.0.custom_id: String should have at most 64 characters'}} text and the smallest action that reproduces it.
Can I ignore this error?
No. Treat it as a failed Anthropic API workflow until the root cause is understood.
Is this guaranteed to have one fix?
No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.
How do I know the fix worked?
Rerun the same command, editor action, or request. The fix is working when that action completes without BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'requests.0.custom_id: String should have at most 64 characters'}}.