CekuraBench
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xAIOpenAI

Grok Voice Think Fast 2.0 vs GPT Realtime 2.1

GPT Realtime 2.1 is ahead on reliability, success rate, agent responses, data accuracy, stalled calls and interruption, and Grok Voice Think Fast 2.0 on response time 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
GPT Realtime 2.1
79.3%1st

GPT Realtime 2.1, 12.2 points higher

Success rate

Calls that passed every check.

Grok Think Fast 2.0
76.0%4th
GPT Realtime 2.1
89.0%1st

GPT Realtime 2.1, 13.0 points higher

Agent responses

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

Grok Think Fast 2.0
96.7%4th
GPT Realtime 2.1
99.2%2nd

GPT Realtime 2.1, 2.4 points higher

Data accuracy

Calls where everything the agent saved matched exactly.

Grok Think Fast 2.0
78.9%5th
GPT Realtime 2.1
92.0%1st

GPT Realtime 2.1, 13.1 points higher

Stalled calls

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

Grok Think Fast 2.0
4.5%7th
GPT Realtime 2.1
3.3%4th

GPT Realtime 2.1, 1.2 points lower

Interruption

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

Grok Think Fast 2.0
4.925th
GPT Realtime 2.1
4.983rd

GPT Realtime 2.1, 0.06 higher

Response time

Median time to start replying after the caller finishes.

Grok Think Fast 2.0
1.62s2nd
GPT Realtime 2.1
1.94s3rd

Grok Think Fast 2.0, 0.31s sooner

Cost / min

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

Grok Think Fast 2.0
$0.0804th
GPT Realtime 2.1
$0.0855th

Grok Think Fast 2.0, $0.005 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, GPT Realtime 2.1 1.94s 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

  • Only a handful of scenarios ever fail, and rarely twice.
  • Best realtime model on the long form, level with the cascade.
  • Few data errors: a phone number or an earlier reference, wrong or left out.
  • Weakest on noisy lines.
Model
gpt-realtime-2.1
Setting
Reasoning high
Voice
marin
Turn taking
Service turn detection
Audio
24 kHz
Cost
Excludes caller transcription, which the service does not meter per call.
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Frequently asked questions

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

Grok Voice Think Fast 2.0 passed 55 of 82 scenarios on all three runs, and GPT Realtime 2.1 passed 65. GPT Realtime 2.1 is ahead, by 12.2 points.

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

Grok Voice Think Fast 2.0 saved everything exactly right on 78.9% of the calls that save data, and GPT Realtime 2.1 on 92.0%. On Appointments, 97.1% against 95.9%. On Medicare, 31.8% against 81.8%. 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?

Grok Voice Think Fast 2.0 starts replying 0.31s 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 takes 1.94s and 2.46s. 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?

Grok Voice Think Fast 2.0 costs $0.080 a minute of call and GPT Realtime 2.1 $0.085, at each vendor's published rates. Grok Voice Think Fast 2.0 is $0.005 cheaper a minute.

How were Grok Voice Think Fast 2.0 and GPT Realtime 2.1 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.