---
profile_id: mcp-2025-11-25
profile_version: 1
assessed_at: 2026-08-15
status: historical-supported
language: en
language_peer: mcp-2025-11-25.zh-CN.md
---

# MCP profile: 2025-11-25

This profile describes implementations that intentionally speak MCP revision `2025-11-25`. It preserves the stateful lifecycle era while incorporating the November 2025 feature and security changes.

## Normative sources

- [Specification index](https://modelcontextprotocol.io/specification/2025-11-25)
- [Key changes from 2025-06-18](https://modelcontextprotocol.io/specification/2025-11-25/changelog)
- [Lifecycle](https://modelcontextprotocol.io/specification/2025-11-25/basic/lifecycle)
- [Transports](https://modelcontextprotocol.io/specification/2025-11-25/basic/transports)
- [Authorization](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization)

Normative requirements remain in the linked specification.

## Protocol shape

- The `initialize` / `notifications/initialized` lifecycle and negotiated protocol version remain authoritative.
- Streamable HTTP still permits optional protocol sessions through `MCP-Session-Id`, request-scoped SSE responses, a GET SSE channel, and resumability with `Last-Event-ID`.
- A present invalid `Origin` has an explicit transport outcome: HTTP `403 Forbidden`.
- Polling SSE is supported: a server may close a connection without terminating its logical stream, while event IDs and retry behavior carry the resumption contract.
- URL-mode elicitation, tool use during sampling, OAuth Client ID Metadata Documents, incremental scope consent, icons, and experimental tasks enter the feature surface.
- JSON Schema 2020-12 is the default dialect for MCP schema definitions.
- Input validation failures during a tool call are tool execution errors so a model can correct arguments; they are not automatically protocol errors.

## Streamable HTTP obligations

- Use one MCP endpoint for POST and GET.
- Validate `Origin`; if it is present and invalid, return HTTP 403. A missing `Origin` is not identical to an invalid present value—define policy separately.
- Require `Accept` negotiation and a single JSON-RPC message per POST.
- Return HTTP 202 without a body for an accepted notification or response.
- Return JSON or a request-scoped SSE stream for a request.
- If implementing polling or resumability, make event IDs identify the originating stream and resume through GET with `Last-Event-ID`.
- If issuing `MCP-Session-Id`, own its generation, secure handling, lookup, expiry, termination, and 404 semantics.
- Send `MCP-Protocol-Version` on subsequent requests; reject unsupported versions.

## Implementation consequences

1. Keep transport session state distinct from application operation state. A session ID is not a substitute for an idempotency key or authorization subject.
2. Model polling SSE as a stateful feature. Closing the TCP connection must not silently discard the logical stream if resumability is claimed.
3. Preserve `stderr` as the logging channel for stdio; `stdout` contains only valid MCP messages.
4. Validate schemas under JSON Schema 2020-12 assumptions and bound recursive/composed schema work.
5. Keep URL elicitation and experimental tasks behind explicit capability declarations and host-compatibility evidence.
6. Treat tool annotations, icons, descriptions, and validation-error classification as behavior visible to both host and model.

## Revision-bound test obligations

- Stateful lifecycle ordering and re-initialization tests.
- Explicit HTTP 403 for a present disallowed `Origin`; exact allowlist echo for permitted cross-origin use.
- No JSON-RPC batch acceptance.
- Notification/response POSTs yield HTTP 202 with no body.
- Session issuance is either absent or backed by secure uniqueness, request validation, expiry, termination, and 404 behavior.
- Polling SSE reconnection preserves stream identity and honors retry timing without replaying another stream's messages.
- Tool input validation failures use the tool-result error channel expected by this revision.
- Experimental task, URL elicitation, and sampling-tool capabilities are absent unless fully implemented and tested with the intended host.

## Migration boundary from 2025-06-18

Do not infer support from a shared lifecycle shape. The explicit invalid-Origin 403 behavior, polling SSE rules, JSON Schema dialect, URL elicitation, sampling tools, registration guidance, and tasks require individual implementation and tests.

## Migration boundary to 2026-07-28

The next revision removes the lifecycle and session architecture this profile depends on. It also removes GET-based general server streams and SSE resumability, replaces server-initiated requests with Multi Round-Trip Requests, requires request metadata in `_meta`, adds `server/discover` and HTTP routing headers, and moves tasks into an extension. See the [2026-07-28 profile](mcp-2026-07-28.md).

Compatibility should be an explicit adapter or negotiated mode. Do not leave old session checks partially active after selecting the stateless revision.

## Known unknowns

- Host support for polling SSE, URL elicitation, experimental tasks, and Client ID Metadata Documents varies.
- A framework may generate or consume session and version headers before application dispatch; inspect the real hook order.
- Authorization topology cannot be proven from application code alone.
- Current ecosystem recommendations may have moved since this profile's assessment date.