Claude Code / AI Coding Tools
Claude Code 2.1.129 sends unsupported anthropic_beta flags in request body that Bedrock rejects with 400
Fix Claude Code sending unsupported beta flags to AWS Bedrock causing 400 errors Includes evidence for Claude Code troubleshooting demand.
- Category
- AI Coding Tools
- Error signature
Anthropic API Error 400: unsupported anthropic_beta flags rejected by Bedrock- Quick fix
- Compare the failing environment with a known working setup, then change one configuration value at a time.
- Updated
What this error means
Anthropic API Error 400: unsupported anthropic_beta flags rejected by Bedrock is a Claude Code failure pattern reported for developers trying to fix claude code sending unsupported beta flags to aws bedrock causing 400 errors. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.
Why this happens
10 reactions. Regression in v2.1.129. Bedrock rejects anthropic_beta flags with 400. Flags: interleaved-thinking-2025-05-14, tool-search-tool-2025-10-19, extended-cache-ttl-2025-04-11. Works on v2.1.119 stable.
Common causes
- Claude Code v2.1.129 regression sends anthropic_beta array (interleaved-thinking, tool-search-tool, extended-cache-ttl) that Bedrock does not recognize, breaking all Bedrock-based Claude Code usage
- 10 reactions. Regression in v2.1.129. Bedrock rejects anthropic_beta flags with 400. Flags: interleaved-thinking-2025-05-14, tool-search-tool-2025-10-19, extended-cache-ttl-2025-04-11. Works on v2.1.119 stable.
Quick fixes
- Confirm the exact error signature matches
Anthropic API Error 400: unsupported anthropic_beta flags rejected by Bedrock. - Check the Claude Code 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: 10 reactions. Regression in v2.1.129. Bedrock rejects anthropic_beta flags with 400. Flags: interleaved-thinking-2025-05-14, tool-search-tool-2025-10-19, extended-cache-ttl-2025-04-11. Works on v2.1.119 stable.
Related errors
- Claude Code Opus 4.7 Bedrock incompatibility
- LiteLLM additional_drop_params ignored
FAQ
What should I check first?
Start with the exact Anthropic API Error 400: unsupported anthropic_beta flags rejected by Bedrock text and the smallest action that reproduces it.
Can I ignore this error?
No. Treat it as a failed Claude Code 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 Anthropic API Error 400: unsupported anthropic_beta flags rejected by Bedrock.