What is SSE transport?
SSE transport is the older MCP remote transport that paired Server-Sent Events for server-to-client streaming with HTTP POST for client requests; it has been superseded by Streamable HTTP.
The SSE (Server-Sent Events) transport was the original way the Model Context Protocol connected to remote servers over a network. It used two channels: a long-lived Server-Sent Events stream over which the server pushed messages to the client, plus separate HTTP POST requests the client used to send its own messages back. SSE is a standard browser-friendly streaming mechanism, which made it a natural first choice, but the two-endpoint design was awkward to scale and to put behind ordinary HTTP infrastructure. The MCP spec deprecated it in favor of Streamable HTTP, which collapses everything onto a single endpoint that can still stream. You will still encounter SSE in the wild: many servers expose a legacy /sse endpoint for backward compatibility, and some older clients only know how to speak SSE, so bridges and config snippets sometimes still reference it. For new deployments, Streamable HTTP is the recommended remote transport.