Grok Voice Think Fast 2.0 is ahead on reliability, success rate, agent responses, data accuracy and response time, and GPT Realtime 2.1 Mini on stalled calls, interruption and cost.
Last updated Methodology by Dileep Chagam
Pick Grok Voice Think Fast 2.0 for reliability across repeated calls (17.1 points higher), calls that pass every check (14.6 points higher), getting the agent's replies right (3.3 points higher), saving the caller's data correctly (14.4 points higher) and fast replies (0.46s sooner). Pick GPT Realtime 2.1 Mini for fewer stalled calls (2.0 points lower), handling interruptions (0.07 higher) and lower cost ($0.060 cheaper).
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, 14.6 points higher
Calls where the agent's replies reached the expected outcome.
Grok Think Fast 2.0, 3.3 points higher
Calls where everything the agent saved matched exactly.
Grok Think Fast 2.0, 14.4 points higher
Calls where the agent went silent for 10 seconds or more.
Realtime 2.1 Mini, 2.0 points lower
How well it handled being talked over, 0 to 5.
Realtime 2.1 Mini, 0.07 higher
Median time to start replying after the caller finishes.
Grok Think Fast 2.0, 0.46s sooner
One minute of call at the vendor's published rates.
Realtime 2.1 Mini, $0.060 cheaper
The small figure is the place among ranked models. The cascade is not ranked.
Grok Think Fast 2.0 1.62s, Realtime 2.1 Mini 2.08s at the median.
Grok Voice Think Fast 2.0 is more reliable, by 17.1 points. Grok Voice Think Fast 2.0 passed 55 of 82 scenarios on all three runs, and GPT Realtime 2.1 Mini passed 41. A scenario only counts when every run of it passed.
For a phone agent, Grok Voice Think Fast 2.0, since it gets more scenarios right on every run. Grok Voice Think Fast 2.0 is ahead on reliability, success rate, agent responses, data accuracy and response time, and GPT Realtime 2.1 Mini on stalled calls, interruption and cost.
Grok Voice Think Fast 2.0, by 14.4 points. Grok Voice Think Fast 2.0 saved everything exactly right on 78.9% of the calls that save data, and GPT Realtime 2.1 Mini on 64.5%. On Appointments, 97.1% against 88.8%. On Medicare, 31.8% against 0.0%. A call counts only when nothing is missing, wrong, extra or saved twice.
Yes. Grok Voice Think Fast 2.0 starts replying 0.46s sooner at the median. Grok Voice Think Fast 2.0 takes 1.62s at the median and 1.94s at p90; GPT Realtime 2.1 Mini takes 2.08s and 2.75s. Both are measured on the call audio, from the caller finishing to the agent starting to reply.
GPT Realtime 2.1 Mini, by 0.07 on a 0 to 5 scale. Grok Voice Think Fast 2.0 scores 4.92 and GPT Realtime 2.1 Mini 4.99 for how well the agent handled being talked over.
GPT Realtime 2.1 Mini, by 2.0 points. The agent went silent for 10 seconds or more on 4.5% of Grok Voice Think Fast 2.0 calls and 2.5% of GPT Realtime 2.1 Mini calls.
GPT Realtime 2.1 Mini is $0.060 cheaper a minute. Grok Voice Think Fast 2.0 costs $0.080 a minute of call and GPT Realtime 2.1 Mini $0.020, at each vendor's published rates.
Cekura ran both as the whole agent in the same open-source Pipecat pipeline, with the same prompt, tools and connection. A simulated caller worked through all 82 scenarios on live calls, three times each, 2,952 calls across the benchmark. A call passes only when the agent said the right things and saved the right data.
