What’s actually changing
The specification changelog states both halves of this change:
“All results now carry mandatory
resultType:completeorinput_required”
“Multi Round-Trip Requests (MRTR) pattern replaces server-initiated requests; servers return
InputRequiredResultwithresultType: input_requiredandinputRequestsfield”
A real example of the interim result shape:
{
"resultType": "input_required",
"inputRequests": {
"confirm": {
"type": "elicitation",
"message": "Delete 3 files?",
"schema": { "type": "boolean" }
}
},
"requestState": "eyJzdGVwIjoxLCJmaWxlcyI6WyJhIiwiYiIsImMiXX0="
}inputRequests is a map of server-initiated requests the client must resolve. requestState is an opaque blob the client echoes back unmodified on the follow-up call, carrying whatever internal progress state the server needs to resume, without the client needing to understand its contents.
Structural Comparison Matrix
| Operational Aspect | Before (pre-2026-07-28) | After (2026-07-28+) |
|---|---|---|
resultType field | Not present on ordinary results | Mandatory: "complete" or "input_required" |
| Mid-call server-initiated requests | A separate server-to-client request pattern | An InputRequiredResult returned from the original call |
| Resuming after input is provided | N/A | Client re-issues the call, echoing requestState unmodified |
Fix it: handle both branches, on both ends
This breaks both servers and clients that skip it
A server that doesn’t set resultType on its ordinary results is sending
malformed responses under this spec. A client that doesn’t branch on
resultType: "input_required" will either crash on the unfamiliar shape or
silently treat an interim result as a final one, neither of which is correct.
{
"resultType": "complete",
"content": [{ "type": "text", "text": "3 files deleted." }]
}Client-side handling needs an explicit branch: check resultType, and if it’s "input_required", resolve every entry in inputRequests, then re-issue the original call with the answers and the untouched requestState. Server-side, every result-returning code path needs the field added, not just the new interim-result path.
Confirmed version
Sourced from the official Model Context Protocol specification changelog, 2026-07-28 revision, published 2026-07-28, including a real InputRequiredResult example from the current specification. Browse more posts like this in the AI Productivity archive.
