Grok Voice Think Fast 2.0 is ahead on reliability, agent responses, stalled calls and response time, and Gemini 3.8 Live Extended Thinking on data accuracy and interruption. The two tie on success rate.
Last updated Methodology by Dileep Chagam
Pick Gemini 3.8 Live Extended Thinking for saving the caller's data correctly (5.5 points higher) and handling interruptions (0.03 higher). Pick Grok Voice Think Fast 2.0 for reliability across repeated calls (14.6 points higher), getting the agent's replies right (8.1 points higher), fewer stalled calls (0.8 points lower) and fast replies (0.45s sooner). They are level on calls that pass every check.
Scenarios that passed on all three runs.
Grok Think Fast 2.0, 14.6 points higher
Calls that passed every check.
Level
Calls where the agent's replies reached the expected outcome.
Grok Think Fast 2.0, 8.1 points higher
Calls where everything the agent saved matched exactly.
Gemini 3.8 Live Thinking, 5.5 points higher
Calls where the agent went silent for 10 seconds or more.
Grok Think Fast 2.0, 0.8 points lower
How well it handled being talked over, 0 to 5.
Gemini 3.8 Live Thinking, 0.03 higher
Median time to start replying after the caller finishes.
Grok Think Fast 2.0, 0.45s 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, Gemini 3.8 Live Thinking 2.07s at the median.
Grok Voice Think Fast 2.0 is more reliable, by 14.6 points. Gemini 3.8 Live Extended Thinking passed 43 of 82 scenarios on all three runs, and Grok Voice Think Fast 2.0 passed 55. 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, agent responses, stalled calls and response time, and Gemini 3.8 Live Extended Thinking on data accuracy and interruption. The two tie on success rate.
Gemini 3.8 Live Extended Thinking, by 5.5 points. Gemini 3.8 Live Extended Thinking saved everything exactly right on 84.4% of the calls that save data, and Grok Voice Think Fast 2.0 on 78.9%. On Appointments, 88.9% against 97.1%. On Medicare, 72.7% against 31.8%. A call counts only when nothing is missing, wrong, extra or saved twice.
No. Grok Voice Think Fast 2.0 starts replying 0.45s sooner at the median. Gemini 3.8 Live Extended Thinking takes 2.07s at the median and 2.74s at p90; Grok Voice Think Fast 2.0 takes 1.62s and 1.94s. Both are measured on the call audio, from the caller finishing to the agent starting to reply.
Gemini 3.8 Live Extended Thinking, by 0.03 on a 0 to 5 scale. Gemini 3.8 Live Extended Thinking scores 4.95 and Grok Voice Think Fast 2.0 4.92 for how well the agent handled being talked over.
Grok Voice Think Fast 2.0, by 0.8 points. The agent went silent for 10 seconds or more on 5.3% of Gemini 3.8 Live Extended Thinking calls and 4.5% of Grok Voice Think Fast 2.0 calls.
There is no verified per-minute rate for Gemini 3.8 Live Extended Thinking, so cost cannot be compared yet.
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.
