overview

 
 ### Messages API
 
-Pass the upstream MCP server's URL in the `mcp_servers` array, the same way as any other remote MCP server. The request body and `anthropic-beta` header follow the standard [MCP connector](https://platform.claude.com/docs/en/agents-and-tools/mcp-connector) format; only the `url` is tunnel-specific. The following example uses the MCP connector's `mcp-client` beta header, which is separate from the `mcp-tunnels` beta used by the [Tunnels API](https://platform.claude.com/docs/en/agents-and-tools/mcp-tunnels/reference). Use an API key for the workspace the tunnel was created in (Console **Settings > API keys**).
+Pass the upstream MCP server's URL in the `mcp_servers` array, the same way as any other remote MCP server. The request body and `anthropic-beta` header follow the standard [MCP connector](https://platform.claude.com/docs/en/agents-and-tools/mcp-connector) format; only the `url` is tunnel-specific. The following example uses the MCP connector's `mcp-client` beta header, which is separate from the `mcp-tunnels` beta used by the [Tunnels API](https://platform.claude.com/docs/en/agents-and-tools/mcp-tunnels/reference). Make the request in the workspace the tunnel was created in by using an API key for that workspace or, if your key has access to multiple workspaces, by setting the [`anthropic-workspace-id` header](https://platform.claude.com/docs/en/manage-claude/authentication#select-a-workspace) to that workspace.
 
 The URL's host is `<subdomain>.<your-tunnel-domain>`. The path depends on your upstream MCP server, not the tunnel: FastMCP's `streamable-http` transport serves at `/mcp`, and other servers may use `/` or a custom path (check the server's documentation). The proxy forwards the path untouched.