115 pages for initialize.

Lifecycle Model Context Protocol · in the page specification/2025-11-25/basic/lifecycle …erver: Initialization Phase activate Client Client->>+Server: initialize request Server-->>Client: initialize response Client--)Server: initialized notification Note over Client,S… Transports Model Context Protocol · in the page specification/2025-11-25/basic/transports …in an `MCP-Session-Id` header on the HTTP response containing the `InitializeResult`. * The session ID **SHOULD** be globally unique and cryptographically secure (e.g., a securely generated… Cancellation Model Context Protocol · in the page specification/2025-11-25/basic/utilities/cancellation …the same direction * Are believed to still be in-progress 2. The `initialize` request **MUST NOT** be cancelled by clients 3. For [task-augmented requests](./tasks), the `tasks/cancel` request **M… Schema Reference Model Context Protocol · in the page specification/2025-11-25/schema …pography"><p>Optional default value.</p> </div></section> </div> ## `initialize` <div class="type"> ### `InitializeRequest` <div class="tsd-signature"><span class="tsd-signature-keyword">interf… Overview Model Context Protocol · in the page specification/2026-07-28/basic/transports/index …r protocol revisions established a connection-scoped session with an `initialize` handshake and allowed servers to initiate JSON-RPC requests. Clients and servers that interoperate with those revision… stdio Model Context Protocol · in the page specification/2026-07-28/basic/transports/stdio …request-metadata) MCP versions and a legacy version that requires an `initialize` handshake **SHOULD** probe with [`server/discover`][server-discover] before sending any other request, setting its pre… Streamable HTTP Model Context Protocol · in the page specification/2026-07-28/basic/transports/streamable-http …request-metadata) MCP versions and a legacy version that requires an `initialize` handshake **MAY** detect which era the server implements by attempting a modern request first. On `400 Bad Request`, t… Versioning and Compatibility Model Context Protocol · in the page specification/2026-07-28/basic/versioning …. * **Legacy**: protocol versions that establish a session with an `initialize` handshake (`2025-11-25` and earlier). * **Dual-era**: an implementation that supports both modern and legacy version… Key Changes Model Context Protocol · in the page specification/2026-07-28/changelog …modelcontextprotocol/pull/2567)). 2. Make MCP stateless: remove the `initialize`/`notifications/initialized` handshake. Every request now carries its protocol version and client capabilities in `_met… Discovery Model Context Protocol · in the page specification/2026-07-28/server/discover …client that supports both modern (per-request `_meta`) and legacy (`initialize` handshake) servers **SHOULD** send `server/discover` first; see [stdio: Backward Compatibility](/specification/202… Overview Model Context Protocol · in the page specification/draft/basic/transports/index …r protocol revisions established a connection-scoped session with an `initialize` handshake and allowed servers to initiate JSON-RPC requests. Clients and servers that interoperate with those revision… stdio Model Context Protocol · in the page specification/draft/basic/transports/stdio …request-metadata) MCP versions and a legacy version that requires an `initialize` handshake **SHOULD** probe with [`server/discover`][server-discover] before sending any other request, setting its pre… Streamable HTTP Model Context Protocol · in the page specification/draft/basic/transports/streamable-http …request-metadata) MCP versions and a legacy version that requires an `initialize` handshake **MAY** detect which era the server implements by attempting a modern request first. On `400 Bad Request`, t… Versioning and Compatibility Model Context Protocol · in the page specification/draft/basic/versioning …. * **Legacy**: protocol versions that establish a session with an `initialize` handshake (`2025-11-25` and earlier). * **Dual-era**: an implementation that supports both modern and legacy version… Discovery Model Context Protocol · in the page specification/draft/server/discover …client that supports both modern (per-request `_meta`) and legacy (`initialize` handshake) servers **SHOULD** send `server/discover` first; see [stdio: Backward Compatibility](/specification/dra…