Initialization

Clients must send a single initialize request per transport connection before invoking any other method on that connection, then acknowledge with an initialized notification. Requests sent before initialization receive a Not initialized error, and repeated initialize calls on the same connection return Already initialized.

The server returns the user agent string it will present to upstream services plus platformFamily and platformOs values that describe the runtime target. Set clientInfo to identify your integration.

initialize.params.capabilities also supports these client capabilities:

• optOutNotificationMethods - exact notification method names to suppress for this connection. Matching is exact (no wildcards or prefixes); unknown names are accepted and ignored.
• requestAttestation - opt into the server-initiated attestation/generate request. Desktop hosts that provide upstream attestation respond with an opaque \{ "token": "..." \} value.
• mcpServerOpenaiFormElicitation - allow downstream MCP servers to send the OpenAI extended-form variant of mcpServer/elicitation/request.

Important: Use clientInfo.name to identify your client for the OpenAI Compliance Logs Platform. If you are developing a new Codex integration intended for enterprise use, please contact OpenAI to get it added to a known clients list. For more context, see the Codex logs reference.

Example (from the Codex VS Code extension):

{
  "method": "initialize",
  "id": 0,
  "params": {
    "clientInfo": {
      "name": "codex_vscode",
      "title": "Codex VS Code Extension",
      "version": "0.1.0"
    }
  }
}

Example with notification opt-out:

{
  "method": "initialize",
  "id": 1,
  "params": {
    "clientInfo": {
      "name": "my_client",
      "title": "My Client",
      "version": "0.1.0"
    },
    "capabilities": {
      "experimentalApi": true,
      "optOutNotificationMethods": ["thread/started", "item/agentMessage/delta"]
    }
  }
}