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

• Claude Code installed
• Anthropic API key (from console.anthropic.com)
• LiteLLM proxy with a virtual key for authentication

Step 1: Configure LiteLLM Proxy

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

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

:::info 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.

:::

:::tip Configure via UI instead of config.yaml

You can also complete this setup from the LiteLLM admin UI:

• Add the model via Models → Add Model, leaving the API Key field blank.
• Enable the toggle at Settings → UI Settings → "Forward LLM provider auth headers".

Both UI actions write to the database and override config.yaml at runtime.

:::

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

# Model name from your config

# 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

Replace sk-12345 with your actual LiteLLM virtual key.

:::tip Multiple headers

For multiple headers, use newline-separated values:

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

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.

Related

• Forward Client Headers — Full BYOK and header forwarding docs
• Claude Code Max Subscription — Using Claude Code with OAuth/Max subscription through LiteLLM