Model Context Protocol
Model Context Protocol, maintained by MCP maintainers under the Agentic AI Foundation. A JSON-RPC 2.0 protocol between hosts, clients and servers; servers offer tools, resources and prompts, and clients may offer elicitation. Status: Current revision 2026-07-28 (released 28 Jul 2026); prior revision 2025-11-25. Registry in preview with API v0.1 frozen since 24 Oct 2025.
Fact sheet
| Name | Model Context Protocol (MCP) |
|---|---|
| Maintainer | MCP maintainers under the Agentic AI Foundation |
| What it is | A JSON-RPC 2.0 protocol between hosts, clients and servers; servers offer tools, resources and prompts, and clients may offer elicitation. |
| Status and version | Current revision 2026-07-28 (released 28 Jul 2026); prior revision 2025-11-25. Registry in preview with API v0.1 frozen since 24 Oct 2025. |
| What it does not do | Does not grade servers, verify registry entries, or prescribe a .well-known discovery file in the 2026-07-28 core spec; server cards are still Working Group work. |
Dated facts
- The 2026-07-28 revision removes the initialize handshake and the Mcp-Session-Id header; every request carries protocol version and client capabilities in _meta. (modelcontextprotocol.io, dated 28 July 2026, read 4 November 2026)
- Servers MUST implement server/discover to advertise supported versions, capabilities and identity. (modelcontextprotocol.io, read 4 November 2026)
- The standard transports are stdio and Streamable HTTP. (modelcontextprotocol.io, read 4 November 2026)
- HTTP+SSE is listed as a deprecated feature since 2025-03-26, with Streamable HTTP as its replacement. (modelcontextprotocol.io, dated 26 March 2025, read 5 November 2026)
- The 2026-07-28 revision adds a feature lifecycle and deprecation policy with Active, Deprecated and Removed states and a minimum twelve-month deprecation window. (modelcontextprotocol.io, read 4 November 2026)
- MCP servers MUST implement OAuth 2.0 Protected Resource Metadata (RFC 9728); clients and authorization servers SHOULD support Client ID Metadata Documents. (modelcontextprotocol.io, read 4 November 2026)
- Dynamic Client Registration (RFC 7591) is deprecated as a registration mechanism and kept for backwards compatibility. (modelcontextprotocol.io, read 4 November 2026)
- Clients MUST send the resource parameter (RFC 8707) in authorization and token requests and MUST validate a present iss parameter (RFC 9207). (modelcontextprotocol.io, read 4 November 2026)
- tools/list, prompts/list and resources/list results now carry required ttlMs and cacheScope fields. (modelcontextprotocol.io, read 4 November 2026)
- Roots, Sampling and Logging are deprecated in 2026-07-28. (modelcontextprotocol.io, read 4 November 2026)
- The 2025-11-25 revision added Client ID Metadata Documents, URL mode elicitation, icons and experimental tasks. (modelcontextprotocol.io, dated 25 November 2025, read 4 November 2026)
- The registry namespaces servers with reverse DNS or io.github.<user> and verifies them by GitHub OAuth or OIDC, DNS or HTTP. (github.com, read 4 November 2026)
Seen in the shared crawl
| Path | Top 10,000 found | Ora leaderboard found |
|---|---|---|
/.well-known/mcp.json | 19 of 7,470 (0.25%) | 66 of 3,366 (1.96%) |
A path counts only when the answer is the right kind of document. Many sites answer these paths with an ordinary web page, which is not counted. See the census.