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Claude Code with Bring Your Own Key (BYOK)

Use Claude Code with your own Anthropic API key through the LiteLLM proxy. When you use Claude's /login with your Anthropic account, your API key is sent as x-api-key. With BYOK enabled, LiteLLM forwards your key to Anthropic instead of using proxy-configured keys — so you pay Anthropic directly while still benefiting from LiteLLM's routing, logging, and guardrails.

How It Works​

  1. Claude Code /login — You sign in with your Anthropic account; Claude Code sends your Anthropic API key as x-api-key.
  2. LiteLLM authentication — You pass your LiteLLM proxy key via ANTHROPIC_CUSTOM_HEADERS so the proxy can authenticate and track your usage.
  3. Key forwarding — With forward_llm_provider_auth_headers: true, LiteLLM forwards your x-api-key to Anthropic, giving it precedence over any proxy-configured keys.

Prerequisites​

Step 1: Configure LiteLLM Proxy​

Enable forwarding of LLM provider auth headers so your Anthropic key takes precedence:

config.yaml
model_list:
  - model_name: claude-sonnet-4-5
    litellm_params:
      model: anthropic/claude-sonnet-4-5
      # No api_key needed — client's key will be used

litellm_settings:
  forward_llm_provider_auth_headers: true  # Required for BYOK
Why forward_llm_provider_auth_headers?

By default, LiteLLM strips x-api-key from client requests for security. Setting this to true allows client-provided provider keys (like your Anthropic key from /login) to be forwarded to Anthropic, overriding any proxy-configured keys.

Step 2: Create a LiteLLM Virtual Key​

Create a virtual key in the LiteLLM UI or via API.

# Example: Create key via API
curl -X POST "http://localhost:4000/key/generate" \
  -H "Authorization: Bearer sk-your-master-key" \
  -H "Content-Type: application/json" \
  -d '{"key_alias": "claude-code-byok", "models": ["claude-sonnet-4-5"]}'

Step 3: Configure Claude Code​

Set environment variables so Claude Code uses LiteLLM and sends your LiteLLM key for proxy auth:

# Point Claude Code to your LiteLLM proxy
export ANTHROPIC_BASE_URL="http://localhost:4000"

# Model name from your config
export ANTHROPIC_MODEL="claude-sonnet-4-5"

# LiteLLM proxy auth — this is added to every request
# Use x-litellm-api-key so the proxy authenticates you; your Anthropic key goes via x-api-key from /login
export ANTHROPIC_CUSTOM_HEADERS="x-litellm-api-key: sk-12345"

Replace sk-12345 with your actual LiteLLM virtual key.

Multiple headers

For multiple headers, use newline-separated values:

export ANTHROPIC_CUSTOM_HEADERS="x-litellm-api-key: sk-12345
x-litellm-user-id: my-user-id"

Step 4: Sign In with Claude Code​

  1. Launch Claude Code:

    claude

  2. Use /login and sign in with your Anthropic account (or use your API key directly).

  3. Claude Code will send:

    • x-api-key: Your Anthropic API key (from /login)
    • x-litellm-api-key: Your LiteLLM key (from ANTHROPIC_CUSTOM_HEADERS)

  4. LiteLLM authenticates you via x-litellm-api-key, then forwards x-api-key to Anthropic. Your Anthropic key takes precedence over any proxy-configured key.

Summary​

HeaderSourcePurpose
x-api-keyClaude Code /login (Anthropic key)Sent to Anthropic for API calls
x-litellm-api-keyANTHROPIC_CUSTOM_HEADERSProxy authentication, tracking, rate limits

Troubleshooting​

Requests fail with "invalid x-api-key"​

  • Ensure forward_llm_provider_auth_headers: true is set in litellm_settings (or general_settings).
  • Restart the LiteLLM proxy after changing the config.
  • Verify you completed /login in Claude Code so your Anthropic key is being sent.

Proxy returns 401​

  • Check that ANTHROPIC_CUSTOM_HEADERS includes x-litellm-api-key: <your-key>.
  • Ensure the LiteLLM key is valid and has access to the model.

Proxy key is used instead of my Anthropic key​

  • Confirm forward_llm_provider_auth_headers: true is in your config.
  • The setting can be in litellm_settings or general_settings depending on your config structure.
  • Enable debug logging: LITELLM_LOG=DEBUG to see which key is being forwarded.