Blogs›OpenAI›Secure MCP Tunnels
This feature thread tracks the evolution of OpenAI's capabilities for securely connecting private MCP servers to hosted AI products. Initially, the focus was on enabling private servers to be reachable without exposing them to the public internet. This involved developing the Secure MCP Tunnel, which allows customers to run a client within their private environment that establishes an outbound HTTPS connection to OpenAI. This client receives MCP requests, forwards them to local servers, and returns responses through the same connection, preserving the server's private network boundary. The design emphasizes outbound-only connectivity, explicit destination configuration, compatibility with MCP streaming and notifications, and a customer-run, inspectable client. The system also extends to support REST APIs through a feature called Harpoon, enabling controlled access to private APIs without opening inbound network access.
6/26/2026
Introduced Secure MCP Tunnel to enable private MCP servers to be reachable by OpenAI products without exposing them to the public internet. This involved designing an outbound-only HTTPS connection model, a customer-run inspectable client, and support for MCP streaming and authentication flows. Extended this model with Harpoon to provide similar secure connectivity for private REST APIs.