An MCP client begins with initialize, sending its protocol version, capabilities, and client information. The server replies with its supported capabilities and a negotiated version. If the requested version is supported, return that version; otherwise offer a supported version. A client that cannot use the returned version should disconnect. After initialization succeeds, the client sends notifications/initialized before normal tool operations. Scope: MCP specification 2025-11-25. Reviewed September 19, 2026; consult the linked specification when implementing a different revision.