Multi Round-Trip Requests (MRTR)
Multi Round-Trip Requests (MRTR) - The 2026-07-28 pattern that replaces server-initiated requests (elicitation/create, sampling/createMessage, roots/list): when a request needs more input mid-call, the server returns a result with resultType "input_required" carrying the requests it needs answered, and the client retries the original call with the answers attached in inputResponses.
Multi Round-Trip Requests solve the problem that made earlier MCP revisions stateful in practice: a tool sometimes needs something from the user in the middle of a call, and before 2026-07-28 the server delivered that need as a server-initiated request over a held-open bidirectional stream. Under MRTR the flow inverts. The server answers the original request with resultType "input_required" and a list of input requests; the client gathers answers and retries the original request with inputResponses attached. Every result in the new revision carries a resultType field ("complete" for ordinary results), and results from earlier-protocol servers that omit the field are treated as complete.
Related concepts
Sources and verification
Last verified · confidence 1.00.
- Official 2026-07-28 changelog - SEP-2322 introduces the MRTR pattern, InputRequiredResult, and the required resultType field on all results - accessed
- Official MCP blog, 2026-07-28 release - MRTR enables mid-call input (confirmations, missing parameters) over a stateless transport without held-open streams - accessed