---
'@modelcontextprotocol/server': minor
'@modelcontextprotocol/core-internal': minor
---

Serve `input_required` handlers on 2025-era connections: the legacy shim (on by default) converts each embedded request of an `input_required` return into a real server→client request (`elicitation/create`, `sampling/createMessage`, `roots/list`) over the live session — stamped with the originating request's id for stream association — and re-enters the handler with the collected `inputResponses` until a final result. Handlers are written once in the 2026 `inputRequired(...)` style and serve both eras; the previous loud `-32603` failure remains available via `ServerOptions.inputRequired.legacyShim: false`. Knobs: `inputRequired.maxRounds` (default 8) and `inputRequired.roundTimeoutMs` (default 600 000 ms per leg; legs carry a progressToken so a client reporting progress mid-leg resets the leg timeout). Semantics mirror the modern client driver exactly: per-round replaced `inputResponses`, byte-exact `requestState` echo with the verify hook running every round, paced requestState-only rounds, and elicitation accepted content passed through UNVALIDATED (the handler validates via the schema-aware `acceptedContent` overload, exactly as on the 2026 era). URL-mode legs synthesize the `elicitationId` the 2025-11-25 wire requires. Failures surface per family (`tools/call` → `isError` tool result; `prompts/get` / `resources/read` → JSON-RPC error); stateless legacy HTTP degrades to a clean capability refusal; the shim emits no progress of its own (the originating progressToken is the handler's single must-increase stream — the shim never adds a second author to it).

`ctx.mcpReq.requestState` is now a typed accessor: `ctx.mcpReq.requestState<T>()` returns the payload the configured `requestState.verify` hook resolved with (e.g. `createRequestStateCodec.verify` — the hook's return value is now load-bearing; verifiers that are not also decoders should resolve `undefined`), the raw wire string when no hook is configured, or `undefined` when the round carried no state. Code that read the property directly becomes a call: `ctx.mcpReq.requestState` → `ctx.mcpReq.requestState<string>()`. Note the member is now always present (a function), so truthiness no longer means "has state", and it is dropped by JSON serialization of the context.

New typed readers for `inputResponses`, exported from `@modelcontextprotocol/server`: a schema-aware `acceptedContent(responses, key, schema)` overload (validates untrusted accepted content against any synchronous Standard Schema) and `inputResponse(responses, key)` (discriminated `missing | elicit | sampling | roots` view, for decline/cancel detection and the non-elicitation kinds). Content conveniences like text extraction stay in application code as one-liners over the discriminated view.