CekuraBench
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xAIOpenAI

Grok Voice Think Fast 2.0 vs GPT Realtime 2.1 Mini

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.

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Success rate by suite

Appointments59 scenariosMedicare23 scenarios
  • GPT Realtime 2.1OpenAI
    92%
    81%
  • GPT-Live 1 + Sol lowOpenAI
    97%
    49%
  • Gemini 3.8 Live ThinkingGoogle
    82%
    61%
  • Grok Think Fast 2.0xAI
    96%
    25%
  • Gemini 3.1 Flash LiveGoogle
    93%
    32%
  • Phonic v1Phonic
    97%
    14%
  • Realtime 2.1 MiniOpenAI
    84%
    4%
  • Nova 2 SonicAmazon
    80%
    6%
  • Cascade, GPT-4.1Not ranked
    97%
    83%
Each model's share of calls that passed every check, on each suite.

Every metric, side by side

Reliability

Scenarios that passed on all three runs.

Grok Think Fast 2.0
67.1%3rd
Realtime 2.1 Mini
50.0%7th

Grok Think Fast 2.0, 17.1 points higher

Success rate

Calls that passed every check.

Grok Think Fast 2.0
76.0%4th
Realtime 2.1 Mini
61.4%7th

Grok Think Fast 2.0, 14.6 points higher

Agent responses

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

Grok Think Fast 2.0
96.7%4th
Realtime 2.1 Mini
93.5%8th

Grok Think Fast 2.0, 3.3 points higher

Data accuracy

Calls where everything the agent saved matched exactly.

Grok Think Fast 2.0
78.9%5th
Realtime 2.1 Mini
64.5%7th

Grok Think Fast 2.0, 14.4 points higher

Stalled calls

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

Grok Think Fast 2.0
4.5%7th
Realtime 2.1 Mini
2.5%3rd

Realtime 2.1 Mini, 2.0 points lower

Interruption

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

Grok Think Fast 2.0
4.925th
Realtime 2.1 Mini
4.992nd

Realtime 2.1 Mini, 0.07 higher

Response time

Median time to start replying after the caller finishes.

Grok Think Fast 2.0
1.62s2nd
Realtime 2.1 Mini
2.08s5th

Grok Think Fast 2.0, 0.46s sooner

Cost / min

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

Grok Think Fast 2.0
$0.0804th
Realtime 2.1 Mini
$0.0201st

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 answers first

Grok Think Fast 2.0 1.62s, Realtime 2.1 Mini 2.08s at the median.

Response time, median to p90

MedianTo p90
Medianp90
  • Phonic v1Phonic
    Phonic v1: median 1.59s, p90 1.86s
    1.59s1.86s
  • Grok Think Fast 2.0xAI
    Grok Think Fast 2.0: median 1.62s, p90 1.94s
    1.62s1.94s
  • GPT Realtime 2.1OpenAI
    GPT Realtime 2.1: median 1.94s, p90 2.46s
    1.94s2.46s
  • GPT-Live 1 + Sol lowOpenAI
    GPT-Live 1 + Sol low: median 2.02s, p90 2.42s
    2.02s2.42s
  • Realtime 2.1 MiniOpenAI
    Realtime 2.1 Mini: median 2.08s, p90 2.75s
    2.08s2.75s
  • Nova 2 SonicAmazon
    Nova 2 Sonic: median 2.18s, p90 2.76s
    2.18s2.76s
  • Gemini 3.8 Live ThinkingGoogle
    Gemini 3.8 Live Thinking: median 2.32s, p90 3.06s
    2.32s3.06s
  • Gemini 3.1 Flash LiveGoogle
    Gemini 3.1 Flash Live: median 2.88s, p90 4.00s
    2.88s4.00s
  • Cascade, GPT-4.1Not ranked
    Cascade, GPT-4.1: median 2.17s, p90 2.51s
    2.17s2.51s
2.0s3.0s4.0s
Seconds from the caller finishing to the agent starting to reply, per model.

What we saw on the calls

Grok Voice Think Fast 2.0

  • Quick, with the shortest replies of the field; steady on the short form.
  • Struggles on the long form: fields left out or wrong, usually an earlier reference.
  • Every stall was on a long form.
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.

GPT Realtime 2.1 Mini

  • Gets most short-form calls right, at a fraction of the cost.
  • Sometimes mishears a phone number.
  • Drops details given earlier: not one long-form record was exact.
  • Rarely recovers when a tool returns an error.
Model
gpt-realtime-2.1-mini
Setting
Reasoning high
Voice
marin
Turn taking
Service turn detection
Audio
24 kHz
Cost
Averaged over the calls with a usage record.
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Frequently asked questions

Is Grok Voice Think Fast 2.0 or GPT Realtime 2.1 Mini more reliable?

Grok Voice Think Fast 2.0 passed 55 of 82 scenarios on all three runs, and GPT Realtime 2.1 Mini passed 41. Grok Voice Think Fast 2.0 is ahead, by 17.1 points.

Which saves caller data more accurately, Grok Voice Think Fast 2.0 or GPT Realtime 2.1 Mini?

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.

Which responds faster, Grok Voice Think Fast 2.0 or GPT Realtime 2.1 Mini?

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.

Which costs less, Grok Voice Think Fast 2.0 or GPT Realtime 2.1 Mini?

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. GPT Realtime 2.1 Mini is $0.060 cheaper a minute.

How were Grok Voice Think Fast 2.0 and GPT Realtime 2.1 Mini compared?

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.