Quick answer: OpenAI owns more of a phone call’s path: its Realtime API and GPT-Live accept 8 kHz G.711 μ-law and terminate SIP; Gemini 3.8 Live takes PCM over a WebSocket and returns 24 kHz audio you must re-encode. A 5-minute call cost $0.29–$0.43 on Gemini 3.8 Live, $0.25 plus backend on GPT-Live 1, and $0.14–$1.87 on OpenAI’s token-billed models.
What this covers
- Gemini Live API vs OpenAI Realtime API: which is better for a phone voice agent?
- The Three-Seam Test: the criteria that decide it on a phone line
- The comparison table, telephony criteria first
- Who resamples the audio: 8 kHz μ-law on each API
- How long can one phone call last on each API?
This is a technical summary. The full guide — with the tables and worked examples — is on our site: *Gemini Live vs OpenAI Realtime for Phone Agents*.
Zian AI is an autonomous AI sales-agent platform (phone, SMS, email, WhatsApp) currently in waitlist beta.
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