Grok Voice Think Fast 2.0 is ahead on reliability, success rate, agent responses, data accuracy and response time, and Amazon Nova 2 Sonic on stalled calls and interruption.
Scenarios that passed on all three runs.
Grok Think Fast 2.0, 17.1 points higher
Calls that passed every check.
Grok Think Fast 2.0, 16.7 points higher
Calls where the agent's replies reached the expected outcome.
Grok Think Fast 2.0, 2.8 points higher
Calls where everything the agent saved matched exactly.
Grok Think Fast 2.0, 19.0 points higher
Calls where the agent went silent for 10 seconds or more.
Nova 2 Sonic, 3.3 points lower
How well it handled being talked over, 0 to 5.
Nova 2 Sonic, 0.07 higher
Median time to start replying after the caller finishes.
Grok Think Fast 2.0, 0.56s sooner
One minute of call at the vendor's published rates.
Not comparable
The small figure is the place among ranked models. The cascade is not ranked.
Grok Think Fast 2.0 1.62s, Nova 2 Sonic 2.18s at the median.
Grok Voice Think Fast 2.0 passed 55 of 82 scenarios on all three runs, and Amazon Nova 2 Sonic passed 41. Grok Voice Think Fast 2.0 is ahead, by 17.1 points.
Grok Voice Think Fast 2.0 saved everything exactly right on 78.9% of the calls that save data, and Amazon Nova 2 Sonic on 59.9%. On Appointments, 97.1% against 82.5%. On Medicare, 31.8% against 1.5%. A call counts only when nothing is missing, wrong, extra or saved twice.
Grok Voice Think Fast 2.0 starts replying 0.56s sooner at the median. Grok Voice Think Fast 2.0 takes 1.62s at the median and 1.94s at p90; Amazon Nova 2 Sonic takes 2.18s and 2.76s. Both are measured on the call audio, from the caller finishing to the agent starting to reply.
There is no verified per-minute rate for Amazon Nova 2 Sonic, so cost cannot be compared yet.
Both ran as the whole agent in the same open-source Pipecat pipeline, with the same prompt, tools and phone line. A simulated caller worked through all 82 scenarios on live calls, three times each, 2,214 calls across the benchmark. A call passes only when the agent said the right things and saved the right data.
