## Fork session

**post** `/live/sessions/{session_id}/fork`

Fork a stored Live session onto a new WebRTC connection.

### Path Parameters

- `session_id: string`

### Body Parameters

- `transport: object { sdp, type }`

  WebRTC transport with an SDP offer for the new connection to the forked session.

  - `sdp: string`

    Session Description Protocol message for the WebRTC connection.

  - `type: "webrtc"`

    The transport used for the Live session. Always `webrtc`.

    - `"webrtc"`

- `session: optional MediaSessionForkConfig`

  Optional configuration overrides for the new Live session. Omit this object or send an empty object to inherit the stored session's settings.

  - `client: optional ClientConfig`

    Startup-only capabilities for an untrusted frontend attached to a unified WebRTC session. Trusted sideband connections are unaffected.

    - `data_channel: DataChannelConfig`

      Client and server event permissions for the WebRTC frontend data channel.

      - `allowed_client_events: optional "all" or array of string`

        Client event types that the frontend data channel may send. Use 'all' to allow every client event; an empty array allows none. Omission preserves the existing allow-all behavior.

        - `"all"`

          - `"all"`

        - `array of string`

      - `allowed_server_events: optional "all" or array of ServerEventSelector`

        Server events that may be sent to the frontend data channel. Use 'all' to allow every server event; an empty array allows none. Omission preserves the existing allow-all behavior. Responses events use an object with type 'response.event' and a response_event selector.

        - `"all"`

          - `"all"`

        - `array of ServerEventSelector`

          - `type: string`

            The outer Live server event type. Use 'response.event' for Responses events.

          - `response_event: optional string`

            The nested Responses event type. Required when type is 'response.event'; forbidden for other event types.

  - `delegation: optional object { type, responses }`

    Update the Responses backend for an existing Live session without changing delegation ownership.

    - `type: "responses"`

      The delegation owner. Always `responses` for tasks handled by the Responses API.

      - `"responses"`

    - `responses: optional ResponsesDelegationUpdateConfig`

      Responses backend settings to update. Omitted settings keep their existing values.

      - `instructions: optional string or null`

        Instructions for the delegated Responses model, separate from Live instructions. See [backend prompting](/api/docs/guides/live-delegation#start-with-your-existing-backend-prompt).

      - `max_output_tokens: optional number or null`

        Maximum number of output tokens for each delegated response.

      - `model: optional string`

        The Responses backend model to use for subsequent delegated requests. Omit to keep the current backend model.

      - `parallel_tool_calls: optional boolean or null`

        Whether the delegated Responses model may request multiple tool calls in a single response.

      - `reasoning: optional object { effort, summary }  or null`

        Reasoning settings passed to each delegated Responses request.

        - `effort: optional "none" or "minimal" or "low" or 3 more or null`

          How much reasoning effort the delegated Responses model should use. Supported values depend on the backend model.

          - `"none"`

          - `"minimal"`

          - `"low"`

          - `"medium"`

          - `"high"`

          - `"xhigh"`

        - `summary: optional "concise" or "detailed" or "auto" or null`

          The reasoning summary to request from the delegated Responses model, when supported.

          - `"concise"`

          - `"detailed"`

          - `"auto"`

      - `service_tier: optional "auto" or "default" or "fast_tier_temp_pilot" or 3 more or null`

        Service tier for delegated Responses requests.

        - `"auto"`

        - `"default"`

        - `"fast_tier_temp_pilot"`

        - `"flex"`

        - `"priority"`

        - `"ultrafast"`

      - `text: optional object { verbosity }  or null`

        Text generation settings passed to each delegated Responses request.

        - `verbosity: optional "low" or "medium" or "high" or null`

          The amount of detail in text generated by the Responses backend. This does not configure the Live model’s spoken delivery.

          - `"low"`

          - `"medium"`

          - `"high"`

      - `tool_choice: optional "auto" or "none" or "required" or object { name, type }  or object { name, server_label, type }`

        Controls which tool the Responses backend uses when handling a task delegated by the Live model.

        - `LiveToolChoiceEnum = "auto" or "none" or "required"`

          - `"auto"`

          - `"none"`

          - `"required"`

        - `LiveFunctionToolChoiceParam object { name, type }`

          - `name: string`

          - `type: "function"`

            - `"function"`

        - `LiveMCPToolChoiceParam object { name, server_label, type }`

          - `name: string`

          - `server_label: string`

          - `type: "mcp"`

            - `"mcp"`

      - `tools: optional array of FunctionTool or object { type }`

        Tools available to the Responses backend while it handles tasks delegated by the Live model.

        - `FunctionTool object { name, type, description, 2 more }`

          A function tool available to the Responses backend when the Live model delegates a task.

          - `name: string`

            The name the delegated Responses model uses when calling this function.

          - `type: "function"`

            The tool type. Always `function`.

            - `"function"`

          - `description: optional string or null`

            What the function does and when the delegated Responses model should call it.

          - `parameters: optional map[unknown] or null`

            A JSON Schema object describing the arguments accepted by the function.

          - `strict: optional boolean or null`

            Whether the delegated Responses model must follow the function’s parameter schema exactly.

        - `WebSearch object { type }`

          A web search tool available to the Live session’s Responses backend.

          - `type: "web_search"`

            The tool type. Always `web_search`.

            - `"web_search"`

  - `store: optional boolean`

    Whether to store the forked session. Omission inherits the stored session's setting.

### Returns

- `session: object { id }`

  The newly created Live session. Use its ID for session controls and sideband connections.

  - `id: string`

    Opaque session identifier. Preserve the returned value unchanged, including its prefix.

- `transport: object { sdp, type }`

  WebRTC transport with the SDP answer.

  - `sdp: string`

    Session Description Protocol message for the WebRTC connection.

  - `type: "webrtc"`

    The transport used for the Live session. Always `webrtc`.

    - `"webrtc"`

### Example

```http
curl https://api.openai.com/v1/live/sessions/$SESSION_ID/fork \
    -H 'Content-Type: application/json' \
    -H "Authorization: Bearer $OPENAI_API_KEY" \
    -d '{
          "transport": {
            "sdp": "x",
            "type": "webrtc"
          }
        }'
```

#### Response

```json
{
  "session": {
    "id": "id"
  },
  "transport": {
    "sdp": "x",
    "type": "webrtc"
  }
}
```

### Example

```http
curl https://api.openai.com/v1/live/sessions/live_123/fork \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"session":{},"transport":{"type":"webrtc","sdp":"<SDP offer>"}}'
```