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Gemini 3.8 Live Extended Thinking vs Grok Voice Think Fast 2.0

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Gemini 3.8 Live Extended ThinkingGoogle
Wins 2 of 8
Reliability
52.4%
Response time
2.07s
Cost / min
n/a
Grok Voice Think Fast 2.0xAI
Wins 4 of 8
Reliability
67.1%
Response time
1.62s
Cost / min
$0.0800

Grok Voice Think Fast 2.0 is ahead on reliability, agent responses, calls where the agent went quiet 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

Who is better at what

For the wider field, see our pick of the best voice AI APIs for real-time audio.

Gemini 3.8 Live Extended ThinkingGrok Voice Think Fast 2.0
  • Reliability52.4%67.1%
  • Success rate76.0%76.0%
  • Agent responses88.6%96.7%
  • Data accuracy84.4%78.9%
  • Went quiet5.3%4.5%
  • Interruption4.954.92
  • Response time2.07s1.62s
  • Cost / minNo verified rate$0.0800

Reliability on booking and Medicare calls

Scenarios the agent passed on every one of its 3 runs.

Booking callsMedicare calls
  1. 59%
    35%
    Gemini 3.8 Live Extended Thinking
  2. 92%
    4%
    Grok Voice Think Fast 2.0

Related comparisons

Both providers, every model: Google vs xAI

Each model on its own: Gemini 3.8 Live Extended Thinking and Grok Voice Think Fast 2.0

Gemini 3.8 Live Extended Thinking vs Grok Voice Think Fast 2.0 FAQ

  • 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 voice 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, calls where the agent went quiet 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 Booking calls, 88.9% against 97.1%. On Medicare calls, 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 quiet 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, 3,690 calls across the benchmark. A call passes only when the agent said the right things and saved the right data.

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