Compare realtime APIs
Pick up to four APIs from any category and see them side by side.
| Twilio ConversationRelay Twilio | Vapi Vapi | Retell AI Retell AI | |
|---|---|---|---|
| Category | Platforms | Platforms | Platforms |
| Status | GA | GA | GA |
| Est. per minute | $0.08 - 0.12 | $0.09 - 0.15 | $0.09 - 0.31 |
| How that was worked out | $0.07 ConversationRelay + $0.0085 inbound or $0.014 outbound + your own LLM (roughly $0.002-0.03/min depending on model). Assumes STT/TTS are included in the $0.07 as third parties report. | Vapi's estimator: 1,000 minutes = $82-$129 including $50 hosting (so $0.082-$0.129/min before carrier), plus $0.008-$0.014 Twilio. Premium LLMs or voices push higher. | Low: $0.055 infra + GPT 4.1 mini $0.0128 + $0.015 TTS + $0.015 telephony = ~$0.098 (cheaper with nano and BYO telephony). High: Retell's own top of range, e.g. GPT 5.x + ElevenLabs v3 + add-ons. |
| Pricing model | per-minute | per-minute | per-minute |
| Free tier | Twilio trial credit only. | $5 free credits and 1 phone number. | $10 free credits. |
| Connects by | PSTN, SIP, WebSocket | WebRTC, WebSocket, SIP, PSTN | WebRTC, SIP, PSTN, WebSocket |
| Audio in | Phone call; Twilio does STT and sends text to you | Phone (Vapi numbers, Twilio, Vonage, Telnyx, SIP), Daily WebRTC web SDK, WebSocket | Phone (Retell numbers, Twilio, Telnyx, custom SIP), web call SDK, custom LLM WebSocket |
| Audio out | You send text tokens; Twilio does TTS | Same | Same |
| Languages | Many via Google/Deepgram STT and ElevenLabs/Google/Amazon voices; 'multi' auto-detect requires Deepgram + ElevenLabs. | Depends on transcriber/voice chosen. | Depends on chosen voice/LLM; not verified. |
| Latency (vendor claim) | No verified number. | No verified number. | No verified number. |
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| Compliance | HIPAA eligible with a signed BAA (per TwiML docs); Twilio-wide SOC 2/GDPR programs not re-verified here. | SOC 2 Type II per third-party trust listing (security.vapi.ai trust center); HIPAA via $2,000/mo add-on; GDPR page in docs. | SOC 2 Type 1 and Type 2, HIPAA (self-serve BAA at click-agreements.retellai.com), GDPR DPA with SCCs, per Retell docs. |
| Self-hostable | No | No | No |
| Last checked | 2026-10-10 | 2026-10-10 | 2026-10-10 |
| Key numbers and features | |||
| Platform $/min | $0.07 | $0.05 | $0.055 |
| All-in price | No | No | No |
| Entry plan $/mo | $0 | $29 | $0 |
| Free tier | Yes | Yes | Yes |
| Free credit $ | - | $5 | $10 |
| Phone numbers | Yes | Yes | Yes |
| Own LLM | Yes | Yes | Yes |
| Own keys | - | Yes | - |
| No-code | - | - | Yes |
| Recording | Yes | Yes | - |
| Noise cancel | - | - | Yes |
| Smart turns | Yes | - | - |
| Latency ms | - | 500 | 600 |
| Languages | - | - | - |
| Max session min | - | - | - |
| Concurrency | - | 10 | 20 |
| WebRTC | - | Yes | Yes |
| WebSocket | Yes | Yes | Yes |
| Phone / SIP | Yes | Yes | Yes |
| HIPAA | Yes | Yes | Yes |
| SOC 2 | - | Yes | Yes |
| EU data | - | Yes | Yes |
| Self-host | No | No | No |
| Open weights | No | No | No |
| High warnings | 0 | 2 | 1 |