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Claude Code - Managing Anthropic Beta Headers

When using Claude Code with LiteLLM and non-Anthropic providers (Bedrock, Azure AI, Vertex AI), you need to ensure that only supported beta headers are sent to each provider. This guide explains how to add support for new beta headers or fix invalid beta header errors.

What Are Beta Headers?​

Anthropic uses beta headers to enable experimental features in Claude. When you use Claude Code, it may send beta headers like:

anthropic-beta: prompt-caching-scope-2026-01-05,advanced-tool-use-2025-11-20

However, not all providers support all Anthropic beta features. LiteLLM uses anthropic_beta_headers_config.json to manage which beta headers are supported by each provider.

Common Error Message​

Error: The model returned the following errors: invalid beta flag

How LiteLLM Handles Beta Headers​

LiteLLM uses a strict validation approach with a configuration file:

litellm/litellm/anthropic_beta_headers_config.json

This JSON file contains a mapping of beta headers for each provider:

  • Keys: Input beta header names (from Anthropic)
  • Values: Provider-specific header names (or null if unsupported)
  • Validation: Only headers present in the mapping with non-null values are forwarded

This enforces stricter validation than just filtering unsupported headers - headers must be explicitly defined to be allowed.

Adding Support for a New Beta Header​

When Anthropic releases a new beta feature, you need to add it to the configuration file for each provider.

Step 1: Locate the Config File​

Find the file in your LiteLLM installation:

# If installed via pip
cd $(python -c "import litellm; import os; print(os.path.dirname(litellm.__file__))")

# The config file is at:
# litellm/anthropic_beta_headers_config.json

Step 2: Add the New Beta Header​

Open anthropic_beta_headers_config.json and add the new header to each provider's mapping:

anthropic_beta_headers_config.json
{
  "description": "Mapping of Anthropic beta headers for each provider. Keys are input header names, values are provider-specific header names (or null if unsupported). Only headers present in mapping keys with non-null values can be forwarded.",
  "anthropic": {
    "advanced-tool-use-2025-11-20": "advanced-tool-use-2025-11-20",
    "new-feature-2026-03-01": "new-feature-2026-03-01",
    ...
  },
  "azure_ai": {
    "advanced-tool-use-2025-11-20": "advanced-tool-use-2025-11-20",
    "new-feature-2026-03-01": "new-feature-2026-03-01",
    ...
  },
  "bedrock_converse": {
    "advanced-tool-use-2025-11-20": "tool-search-tool-2025-10-19",
    "new-feature-2026-03-01": null,
    ...
  },
  "bedrock": {
    "advanced-tool-use-2025-11-20": "tool-search-tool-2025-10-19",
    "new-feature-2026-03-01": null,
    ...
  },
  "vertex_ai": {
    "advanced-tool-use-2025-11-20": "tool-search-tool-2025-10-19",
    "new-feature-2026-03-01": null,
    ...
  }
}

Key Points:

  • Supported headers: Set the value to the provider-specific header name (often the same as the key)
  • Unsupported headers: Set the value to null
  • Header transformations: Some providers use different header names (e.g., Bedrock maps advanced-tool-use-2025-11-20 to tool-search-tool-2025-10-19)
  • Alphabetical order: Keep headers sorted alphabetically for maintainability

Step 3: Restart Your Application​

After updating the config file, restart your LiteLLM proxy or application:

# If using LiteLLM proxy
litellm --config config.yaml

# If using Python SDK
# Just restart your Python application

The updated configuration will be loaded automatically.

Fixing Invalid Beta Header Errors​

If you encounter an "invalid beta flag" error, it means a beta header is being sent that the provider doesn't support.

Step 1: Identify the Problematic Header​

Check your logs to see which header is causing the issue:

Error: The model returned the following errors: invalid beta flag: new-feature-2026-03-01

Step 2: Update the Config​

Set the header value to null for that provider:

anthropic_beta_headers_config.json
{
  "bedrock_converse": {
    "new-feature-2026-03-01": null
  }
}

Step 3: Restart and Test​

Restart your application and verify the header is now filtered out.

Contributing a Fix to LiteLLM​

Help the community by contributing your fix!

What to Include in Your PR​

  1. Update the config file: Add the new beta header to litellm/anthropic_beta_headers_config.json
  2. Test your changes: Verify the header is correctly filtered/mapped for each provider
  3. Documentation: Include provider documentation links showing which headers are supported

Example PR Description​

## Add support for new-feature-2026-03-01 beta header

### Changes
- Added `new-feature-2026-03-01` to anthropic_beta_headers_config.json
- Set to `null` for bedrock_converse (unsupported)
- Set to header name for anthropic, azure_ai (supported)

### Testing
Tested with:
- ✅ Anthropic: Header passed through correctly
- ✅ Azure AI: Header passed through correctly  
- ✅ Bedrock Converse: Header filtered out (returns error without fix)

### References
- Anthropic docs: [link]
- AWS Bedrock docs: [link]

How Beta Header Filtering Works​

When you make a request through LiteLLM:

Filtering Rules​

  1. Header must exist in mapping: Unknown headers are filtered out
  2. Header must have non-null value: Headers with null values are filtered out
  3. Header transformation: Headers are mapped to provider-specific names (e.g., advanced-tool-use-2025-11-20 → tool-search-tool-2025-10-19 for Bedrock)

Example​

Request with headers:

anthropic-beta: advanced-tool-use-2025-11-20,computer-use-2025-01-24,unknown-header

For Bedrock Converse:

  • ✅ computer-use-2025-01-24 → computer-use-2025-01-24 (supported, passed through)
  • ❌ advanced-tool-use-2025-11-20 → filtered out (null value in config)
  • ❌ unknown-header → filtered out (not in config)

Result sent to Bedrock:

anthropic-beta: computer-use-2025-01-24

Provider-Specific Notes​

Bedrock​

  • Beta headers appear in both HTTP headers AND request body (additionalModelRequestFields.anthropic_beta)
  • Some headers are transformed (e.g., advanced-tool-use → tool-search-tool)

Azure AI​

  • Uses same header names as Anthropic
  • Some features not yet supported (check config for null values)

Vertex AI​

  • Some headers are transformed to match Vertex AI's implementation
  • Limited beta feature support compared to Anthropic