Claude Opus 4-7 on Bedrock Prepends <<<SENTINEL\n to Tool Input JSON Values

What this error means

claude-opus-4-7 prepends literal <<<SENTINEL\n to every string value in tool input_json is a Anthropic API / AWS Bedrock failure pattern reported for developers trying to fix claude opus 4-7 on bedrock adding <<<sentinel prefix to tool call arguments. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Confirmed across 5+ separate Bedrock inference calls in same thread. Affects claude-opus-4-7 global model. Every string value in tool input_json starts with literal <<<SENTINEL\n bytes. Not present in user prompts, system prompts, or codebase. Appears to be model-side training regression.

Common causes

• Model regression on Bedrock prepends garbage bytes to tool input JSON, corrupting file writes and code generation. Affects production deployments using Bedrock cross-region inference.
• Confirmed across 5+ separate Bedrock inference calls in same thread. Affects claude-opus-4-7 global model. Every string value in tool input_json starts with literal <<<SENTINEL\n bytes. Not present in user prompts, system prompts, or codebase. Appears to be model-side training regression.

Quick fixes

1. Confirm the exact error signature matches claude-opus-4-7 prepends literal <<<SENTINEL\n to every string value in tool input_json.
2. Check the Anthropic API / AWS Bedrock account, local tool state, and provider configuration involved in the failing workflow.
3. 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

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. 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

• https://github.com/anthropics/anthropic-sdk-typescript/issues/1031

Evidence note: Confirmed across 5+ separate Bedrock inference calls in same thread. Affects claude-opus-4-7 global model. Every string value in tool input_json starts with literal <<<SENTINEL\n bytes. Not present in user prompts, system prompts, or codebase. Appears to be model-side training regression.

Related errors

• Anthropic API Bedrock model not found
• Anthropic API rate limit Bedrock

FAQ

What should I check first?

Start with the exact claude-opus-4-7 prepends literal <<<SENTINEL\n to every string value in tool input_json text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Anthropic API / AWS Bedrock 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 claude-opus-4-7 prepends literal <<<SENTINEL\n to every string value in tool input_json.