MCP 2026-07-28: Stateless Tool Call

MCP 2026-07-28: Stateless Tool Call A sequence diagram generated by Archify. call tool get access token access token tools/call + _meta + Bearer validated: run tool tool output result + serverInfo _meta tool result Host · user + approvals · Sequence participant Host user + approvals MCP client · connector · Sequence participant MCP client connector Authorization server · token source · Sequence participant Authorization server token source MCP server · validates every call · Sequence participant MCP server validates every call Tool API · tool backend · Sequence participant Tool API tool backend Legend security async trace default message

Stateless by design

  • • No initialize and no Mcp-Session-Id in the 2026-07-28 core
  • • Request _meta carries protocolVersion, clientCapabilities, clientInfo; the Bearer token is not in _meta, it travels in the Authorization header
  • • Result _meta: io.modelcontextprotocol/serverInfo. Auth only for protected tools; no model in MCP

Auth failure (not drawn: success path only)

  • • 401 unauthenticated / 403 insufficient scope: no tool execution