Cozzo-tested · Oct 20, 2026
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Ultravox vs Retell AI: latency benchmark on real phone calls
On our phone calls, Retell AI replied faster: a 1.04 s median versus 1.18 s for Ultravox, a gap of 0.14 s. On a browser connection (no phone network) the order flips: Ultravox 0.49 s vs 0.76 s for Retell AI.
Bars are scaled within each row, so compare left against right, not across rows.
Show full table
Reply time is the gap from the end of the caller’s speech to the agent’s first reply audio, timed from our recording of real phone calls (Twilio calling each vendor from a US number, Ashburn, Virginia (US East)), on each vendor’s default model and voice, with the same short dental-receptionist script. Twilio added about $0.01/min for the phone leg (SIP dial-out plus recording). Small samples: differences of a few hundredths of a second are noise. Ranking order comes only from the measured medians.
Ultravox
Most of our Ultravox time used its free minutes; the rest is billed at $0.05/min. The total also covers Ultravox acting as our scripted caller, and is our calculation from billed seconds (Ultravox shows no dollar usage).
Its 6.9% phone transcription score comes entirely from missing the caller’s closing “Thanks, bye” before the call ended; the three test questions were transcribed with no errors.
Retell AI
With Retell’s default voice and LLM; Retell lists $0.07–0.31/min depending on the voice and model you pick.
Cozzo-tested · Round 4 · October 22, 2026
AI receptionist test: Ultravox vs Retell AI
Calls passed out of 3 on each scenario, same dental-office prompt for both.
Ultravox · 14/15 · 1.27 s median reply
- Book a new patient
- Reschedule
- Unknown insurance
- Interruption
- Dental emergency
Retell AI · 12/15 · 1.38 s median reply
- Book a new patient
- Reschedule
- Unknown insurance
- Interruption
- Dental emergency
† Callback taken, but the number was read back wrong at least once. 3 calls per scenario; small samples.
See the AI receptionist benchmark →All voice AI benchmarks →
- Full phone-call benchmark: all 8 platforms, method and limits.
- Ultravox Alternatives Compared: other options if this one doesn’t fit.
- Retell AI Pricing Explained: list prices, line by line.
- Retell AI Alternatives Compared: other options if this one doesn’t fit.
- Methodology and how we test.