CekuraBench
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GooglexAI

Gemini 3.1 Flash Live Preview vs Grok Voice Think Fast 2.0

Gemini 3.1 Flash Live Preview is ahead on data accuracy, stalled calls, interruption and cost, and Grok Voice Think Fast 2.0 on reliability, agent responses and response time. The two tie on success rate.

Last updated Methodology by Dileep Chagam

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Success rate by suite

Higher is better
Appointments59 scenariosMedicare23 scenarios
  • Grok Think Fast 2.0xAI
    96%
    25%
  • Gemini 3.1 Flash LiveGoogle
    93%
    32%
Each model's share of calls that passed every check, on each suite.
Verdict

Which to pick

Pick Gemini 3.1 Flash Live Preview for saving the caller's data correctly (0.3 points higher), fewer stalled calls (1.2 points lower), handling interruptions (0.06 higher) and lower cost ($0.010 cheaper). Pick Grok Voice Think Fast 2.0 for reliability across repeated calls (4.9 points higher), getting the agent's replies right (0.8 points higher) and fast replies (1.26s sooner). They are level on calls that pass every check.

Every metric, side by side

Reliability

Scenarios that passed on all three runs.

Gemini 3.1 Flash Live
62.2%6th
Grok Think Fast 2.0
67.1%5th

Grok Think Fast 2.0, 4.9 points higher

Success rate

Calls that passed every check.

Gemini 3.1 Flash Live
76.0%5th
Grok Think Fast 2.0
76.0%5th

Level

Agent responses

Calls where the agent's replies reached the expected outcome.

Gemini 3.1 Flash Live
95.9%6th
Grok Think Fast 2.0
96.7%5th

Grok Think Fast 2.0, 0.8 points higher

Data accuracy

Calls where everything the agent saved matched exactly.

Gemini 3.1 Flash Live
79.2%5th
Grok Think Fast 2.0
78.9%6th

Gemini 3.1 Flash Live, 0.3 points higher

Stalled calls

Calls where the agent went silent for 10 seconds or more.

Gemini 3.1 Flash Live
3.3%6th
Grok Think Fast 2.0
4.5%8th

Gemini 3.1 Flash Live, 1.2 points lower

Interruption

How well it handled being talked over, 0 to 5.

Gemini 3.1 Flash Live
4.985th
Grok Think Fast 2.0
4.929th

Gemini 3.1 Flash Live, 0.06 higher

Response time

Median time to start replying after the caller finishes.

Gemini 3.1 Flash Live
2.88s11th
Grok Think Fast 2.0
1.62s2nd

Grok Think Fast 2.0, 1.26s sooner

Cost / min

One minute of call at the vendor's published rates.

Gemini 3.1 Flash Live
$0.0703rd
Grok Think Fast 2.0
$0.0805th

Gemini 3.1 Flash Live, $0.010 cheaper

The small figure is the place among ranked models. The cascade is not ranked.

Grok Think Fast 2.0 answers first

Grok Think Fast 2.0 1.62s, Gemini 3.1 Flash Live 2.88s at the median.

Response time, median to p90

Lower is betterMedianTo p90
Medianp90
  • Grok Think Fast 2.0xAI
    Grok Think Fast 2.0: median 1.62s, p90 1.94s
    1.62s1.94s
  • Gemini 3.1 Flash LiveGoogle
    Gemini 3.1 Flash Live: median 2.88s, p90 4.00s
    2.88s4.00s
2.0s3.0s4.0s
Seconds from the caller finishing to the agent starting to reply, per model.

What we saw on the calls

Gemini 3.1 Flash Live Preview

  • Reliable on bookings.
All 3 notes on Gemini 3.1 Flash Live
Model
models/gemini-3.1-flash-live-preview
Setting
Thinking level high
Voice
Charon
Turn taking
Shared local turn detection
Audio
16 kHz
Cost
Averaged over the calls with a usage record.

Grok Voice Think Fast 2.0

  • Shortest replies of the field, and steady on bookings.
All 3 notes on Grok Think Fast 2.0
Model
grok-voice-think-fast-2.0
Setting
Reasoning high
Voice
eve
Turn taking
Service turn detection
Audio
24 kHz
Cost
Excludes a text-input charge the vendor lists without a unit.
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Frequently asked questions

Is Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0 more reliable?

Grok Voice Think Fast 2.0 is more reliable, by 4.9 points. Gemini 3.1 Flash Live Preview passed 51 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.

Which should I pick, Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0?

For a phone agent, Grok Voice Think Fast 2.0, since it gets more scenarios right on every run. Gemini 3.1 Flash Live Preview is ahead on data accuracy, stalled calls, interruption and cost, and Grok Voice Think Fast 2.0 on reliability, agent responses and response time. The two tie on success rate.

Which saves caller data more accurately, Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0?

Gemini 3.1 Flash Live Preview, by 0.3 points. Gemini 3.1 Flash Live Preview saved everything exactly right on 79.2% of the calls that save data, and Grok Voice Think Fast 2.0 on 78.9%. On Appointments, 96.5% against 97.1%. On Medicare, 34.8% against 31.8%. A call counts only when nothing is missing, wrong, extra or saved twice.

Is Gemini 3.1 Flash Live Preview faster than Grok Voice Think Fast 2.0?

No. Grok Voice Think Fast 2.0 starts replying 1.26s sooner at the median. Gemini 3.1 Flash Live Preview takes 2.88s at the median and 4.00s 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.

Which handles interruptions better, Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0?

Gemini 3.1 Flash Live Preview, by 0.06 on a 0 to 5 scale. Gemini 3.1 Flash Live Preview scores 4.98 and Grok Voice Think Fast 2.0 4.92 for how well the agent handled being talked over.

Which goes silent on callers less often, Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0?

Gemini 3.1 Flash Live Preview, by 1.2 points. The agent went silent for 10 seconds or more on 3.3% of Gemini 3.1 Flash Live Preview calls and 4.5% of Grok Voice Think Fast 2.0 calls.

Which is cheaper, Gemini 3.1 Flash Live Preview or Grok Voice Think Fast 2.0?

Gemini 3.1 Flash Live Preview is $0.010 cheaper a minute. Gemini 3.1 Flash Live Preview costs $0.070 a minute of call and Grok Voice Think Fast 2.0 $0.080, at each vendor's published rates.

Where does the Gemini 3.1 Flash Live Preview vs Grok Voice Think Fast 2.0 data come from?

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.