Point the SBC at sip:$PROJECT_ID@sip.api.openai.com;transport=tls on TCP port 5061, register a webhook first, and open bidirectional UDP for SRTP to the four published /28 blocks — 64 addresses in total. No SIP password and no IP access control list is documented for you to configure, and the path is inbound only as at 16 September 2026.
What this covers
- The Direct-SIP Cutover Gate: five checks to run before you move traffic
- What the CPaaS was doing that nobody is doing now
- How big is the allowlist, and what does the firewall rule actually say?
- When to go direct, and when to keep something in the middle
- Sources, and who owns each figure
This is a technical summary. The full guide — with the tables and worked examples — is on our site: *Direct SIP AI Voice Agent: No Twilio in the Path*.
Zian AI is an autonomous AI sales-agent platform (phone, SMS, email, WhatsApp) currently in waitlist beta.
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