SIP is a protocol used to make phone calls over the internet. With SIP and the Realtime API you can direct incoming phone calls to the API.

Overview

If you want to connect a phone number to the Realtime API, use a SIP trunking provider (e.g., Twilio). This is a service that converts your phone call to IP traffic. After you purchase a phone number from your SIP trunking provider, follow the instructions below.

Start by creating a webhook for incoming calls, through your platform.openai.com settings > Project > Webhooks. Then, point your SIP trunk at the OpenAI SIP endpoint, using the project ID for which you configured the webhook, e.g., sip:$PROJECT_ID@sip.api.openai.com;transport=tls. To find your $PROJECT_ID, visit settings > Project > General. That page will display the project ID, which will have a proj_ prefix.

When OpenAI receives SIP traffic associated with your project, your webhook will be fired. The event fired will be a realtime.call.incoming event, like the example below:

From this webhook, you can accept or reject the call, using the call_id value from the webhook. When accepting the call, you’ll provide the needed configuration (instructions, voice, etc) for the Realtime API session. Once established, you can set up a WebSocket and monitor the session as usual. The APIs to accept, reject, monitor, refer, and hangup the call are documented below.

Accept the call

Use the Accept call endpoint to approve the inbound call and configure the realtime session that will answer it. Send the same parameters you would send in a create client secret request, i.e., ensure the realtime model, voice, tools, or instructions are set before bridging the call to the model.

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curl -X POST "https://api.openai.com/v1/realtime/calls/$CALL_ID/accept" \
 -H "Authorization: Bearer $OPENAI_API_KEY" \
 -H "Content-Type: application/json" \
 -d '{
 "type": "realtime",
 "model": "gpt-realtime-2",
 "instructions": "You are Alex, a friendly concierge for Example Corp."
 }'

The request path must include the call_id from the realtime.call.incoming webhook, and every request requires the Authorization header shown above. The endpoint returns 200 OK once the SIP leg is ringing and the realtime session is being established.

Reject the call

Use the Reject call endpoint to decline an invite when you do not want to handle the incoming call, (e.g., from an unsupported country code.) Supply the call_id path parameter and an optional SIP status_code (e.g., 486 to indicate “busy”) in the JSON body to control the response sent back to the carrier.

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curl -X POST "https://api.openai.com/v1/realtime/calls/$CALL_ID/reject" \
 -H "Authorization: Bearer $OPENAI_API_KEY" \
 -H "Content-Type: application/json" \
 -d '{"status_code": 486}'

If no status code is supplied the API uses 603 Decline by default. A successful request responds with 200 OK after OpenAI delivers the SIP response.

Monitor call events

After you accept a call, open a WebSocket connection to the same session to stream events and issue realtime commands. Note that when connecting to an existing call using the call_id parameter, the model argument is not used (as it has already been configured via the accept endpoint).

WebSocket request

GET wss://api.openai.com/v1/realtime?call_id={call_id}

Query parameters

Headers

• Authorization: Bearer YOUR_API_KEY

The WebSocket behaves exactly like any other Realtime API connection. Send response.create, and other client events to control the call, and listen for server events to track progress. See Webhooks and server-side controls for more information.

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import WebSocket from"ws";
const callId = "rtc_u1_9c6574da8b8a41a18da9308f4ad974ce";
const ws = new WebSocket(`wss://api.openai.com/v1/realtime?call_id=${callId}`, {
headers: {
Authorization: `Bearer ${process.env.OPENAI_API_KEY}`,
 },
});
ws.on("open", () => {
 ws.send(
JSON.stringify({
type: "response.create",
 })
 );
});

Redirect the call

Transfer an active call using the Refer call endpoint. Provide the call_id as well as the target_uri that should be placed in the SIP Refer-To header (for example tel:+14155550123 or sip:agent@example.com).

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curl -X POST "https://api.openai.com/v1/realtime/calls/$CALL_ID/refer" \
 -H "Authorization: Bearer $OPENAI_API_KEY" \
 -H "Content-Type: application/json" \
 -d '{"target_uri": "tel:+14155550123"}'

OpenAI returns 200 OK once the REFER is relayed to your SIP provider. The downstream system handles the rest of the call flow for the caller.

Hang up the call

End the session with the Hang up endpoint when your application should disconnect the caller. This endpoint can be used to terminate both SIP and WebRTC realtime sessions.

curl -X POST "https://api.openai.com/v1/realtime/calls/$CALL_ID/hangup" \
 -H "Authorization: Bearer $OPENAI_API_KEY"

The API responds with 200 OK when it starts tearing down the call.

Dedicated SIP IP ranges

If you need to allowlist OpenAI SIP traffic. sip.api.openai.com does GeoIP routing, you will be connected to the closest region.

• 13.79.45.80/28 for northeurope
• 23.98.140.64/28 for southcentralus
• 40.67.149.176/28 for eastus2
• 40.83.204.240/28 for westus

Python example

The following is an example of a realtime.call.incoming handler. It accepts the call and then logs all the events from the Realtime API.

Next steps

Now that you’ve connected over SIP, use the left navigation or click into these pages to start building your realtime application.

• Realtime prompting guide
• Managing conversations
• Webhooks and server-side controls
• Managing costs
• Realtime transcription

Additional Resources

• JavaScript demo
• Connect the Realtime SIP Connector to Twilio Elastic SIP Trunking