MRTR: Human-in-the-Loop MCP Tools Over Stateless HTTP

On July 28, 2026 the Model Context Protocol shipped its biggest revision since launch, and one line in the changelog quietly broke a pattern thousands of MCP servers rely on: the server-initiated back-channel is gone. Under SEP-2577, a running tool can no longer reach out mid-execution to ask the user a question. That means ctx.elicit() — the call every “are you sure?” confirmation and every “which folder?” prompt was built on — stops working the moment your connection negotiates the modern protocol.

The replacement is MRTR: Multi Round-Trip Requests (SEP-2322). Instead of blocking inside the tool and waiting on an open stream, a tool now returns a description of what it needs. The client answers, then re-issues the same call with the answer attached, and the tool runs again from the top. Each round is a complete request/response cycle, which is exactly why it survives on stateless, serverless, and load-balanced deployments where no two rounds are guaranteed to hit the same worker.