Realtime session continues after Twilio SIP No Answer

I’ve observed a problem with gpt-realtime sessions using Twilio SIP for the last few weeks, where a session continues despite the Twilio call record showing an SIP call duration of zero seconds and a status of “No Answer”. We receive a webhook notifying our server of the call and we accept the call and connect a websocket to listen for events. Normally, the websocket connection is closed by OpenAI when the Twilio call concludes, and we log the duration of the call. In these cases, the connection stays open for an hour then closes, and we record durations of 3,608 to 3,610 seconds.

Twilio’s recordings of these calls are less than two seconds long, so it appears that the call ends when the SIP request receives No Answer (recording starts just before the call is transferred to SIP). We would expect the call session to end at this point, closing websocket connections and refusing new connections.

Here is a list of UTC datetimes and Twilio call SIDs for some of these calls. In every case, Twilio outgoing dial was made to sip:proj_hQrGn5uofTdGyHoKRjkiKbKN@sip.api.openai.com;transport=tls

2026-04-03 22:45:31 CAe73a7e55664b10ce48d7ce0073b8b970

2026-04-07 14:06:56 CA2014a85aaefe9eb4c70a79e0556c9486

2026-04-07 18:26:37 CA217c730bf75d2c6f7530e9a3c1c691d6

2026-04-10 19:35:25 CA165f547f0558a9490a131b48bab7fd5d

2026-04-12 14:41:17 CA9e3a4538da0bb9eab1c11238eea9e684