CekuraBench
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AmazonCascade baseline

Amazon Nova 2 Sonic vs Flux → GPT-4.1 → ElevenLabs Flash

Flux → GPT-4.1 → ElevenLabs Flash is ahead on reliability, success rate, agent responses, data accuracy, stalled calls and response time, and Amazon Nova 2 Sonic on interruption.

Last updated Methodology by Dileep Chagam

Compare

Success rate by suite

Higher is better
Appointments59 scenariosMedicare23 scenarios
  • 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.
Verdict

Which to pick

Pick Amazon Nova 2 Sonic for handling interruptions (0.03 higher). Pick Flux → GPT-4.1 → ElevenLabs Flash for reliability across repeated calls (32.9 points higher), calls that pass every check (33.7 points higher), getting the agent's replies right (5.3 points higher), saving the caller's data correctly (34.2 points higher), fewer stalled calls (0.4 points lower) and fast replies (0.01s sooner).

Every metric, side by side

Reliability

Scenarios that passed on all three runs.

Nova 2 Sonic
50.0%9th
Cascade, GPT-4.1
82.9%

Cascade, GPT-4.1, 32.9 points higher

Success rate

Calls that passed every check.

Nova 2 Sonic
59.3%11th
Cascade, GPT-4.1
93.1%

Cascade, GPT-4.1, 33.7 points higher

Agent responses

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

Nova 2 Sonic
93.9%9th
Cascade, GPT-4.1
99.2%

Cascade, GPT-4.1, 5.3 points higher

Data accuracy

Calls where everything the agent saved matched exactly.

Nova 2 Sonic
59.9%11th
Cascade, GPT-4.1
94.1%

Cascade, GPT-4.1, 34.2 points higher

Stalled calls

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

Nova 2 Sonic
1.2%2nd
Cascade, GPT-4.1
0.8%

Cascade, GPT-4.1, 0.4 points lower

Interruption

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

Nova 2 Sonic
4.991st
Cascade, GPT-4.1
4.96

Nova 2 Sonic, 0.03 higher

Response time

Median time to start replying after the caller finishes.

Nova 2 Sonic
2.18s9th
Cascade, GPT-4.1
2.17s

Cascade, GPT-4.1, 0.01s sooner

Cost / min

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

Nova 2 Sonic
No verified rate
Cascade, GPT-4.1
No verified rate

Not comparable

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

Cascade, GPT-4.1 answers first

Cascade, GPT-4.1 2.17s, Nova 2 Sonic 2.18s at the median.

Response time, median to p90

Lower is betterMedianTo p90
Medianp90
  • Nova 2 SonicAmazon
    Nova 2 Sonic: median 2.18s, p90 2.76s
    2.18s2.76s
  • Cascade, GPT-4.1Not ranked
    Cascade, GPT-4.1: median 2.17s, p90 2.51s
    2.17s2.51s
2.0s3.0s
Seconds from the caller finishing to the agent starting to reply, per model.

What we saw on the calls

Amazon Nova 2 Sonic

  • Best voice score of the field.
All 3 notes on Nova 2 Sonic
Model
amazon.nova-2-sonic-v1:0
Setting
Endpointing medium
Voice
matthew
Turn taking
Shared local turn detection
Audio
16 kHz
Cost
The vendor's rates for this model are not yet verified.

Flux → GPT-4.1 → ElevenLabs Flash

  • Most scenarios pass every run, and none fails every run.
All 4 notes on Cascade, GPT-4.1
Model
flux-general-en → gpt-4.1 → eleven_flash_v2_5
Setting
No reasoning setting
Voice
ElevenLabs 21m00Tcm4TlvDq8ikWAM
Turn taking
Speech-to-text turn detection
Audio
16 kHz
Cost
Not published: no verified combined rate for the three services.
See the full leaderboardReference agent

Related comparisons

Frequently asked questions

Is Amazon Nova 2 Sonic or Flux → GPT-4.1 → ElevenLabs Flash more reliable?

Flux → GPT-4.1 → ElevenLabs Flash is more reliable, by 32.9 points. Amazon Nova 2 Sonic passed 41 of 82 scenarios on all three runs, and Flux → GPT-4.1 → ElevenLabs Flash passed 68. A scenario only counts when every run of it passed.

Is Amazon Nova 2 Sonic better than a cascaded STT, LLM and TTS pipeline?

On reliability, no: the Flux → GPT-4.1 → ElevenLabs Flash cascade passes more scenarios on every run. Flux → GPT-4.1 → ElevenLabs Flash is ahead on reliability, success rate, agent responses, data accuracy, stalled calls and response time, and Amazon Nova 2 Sonic on interruption. Both ran as the same agent, with the same prompt and tools.

Which saves caller data more accurately, Amazon Nova 2 Sonic or Flux → GPT-4.1 → ElevenLabs Flash?

Flux → GPT-4.1 → ElevenLabs Flash, by 34.2 points. Amazon Nova 2 Sonic saved everything exactly right on 59.9% of the calls that save data, and Flux → GPT-4.1 → ElevenLabs Flash on 94.1%. On Appointments, 82.5% against 98.8%. On Medicare, 1.5% against 81.8%. A call counts only when nothing is missing, wrong, extra or saved twice.

Is Amazon Nova 2 Sonic faster than Flux → GPT-4.1 → ElevenLabs Flash?

No. Flux → GPT-4.1 → ElevenLabs Flash starts replying 0.01s sooner at the median. Amazon Nova 2 Sonic takes 2.18s at the median and 2.76s at p90; Flux → GPT-4.1 → ElevenLabs Flash takes 2.17s and 2.51s. Both are measured on the call audio, from the caller finishing to the agent starting to reply.

Which handles interruptions better, Amazon Nova 2 Sonic or Flux → GPT-4.1 → ElevenLabs Flash?

Amazon Nova 2 Sonic, by 0.03 on a 0 to 5 scale. Amazon Nova 2 Sonic scores 4.99 and Flux → GPT-4.1 → ElevenLabs Flash 4.96 for how well the agent handled being talked over.

Which goes silent on callers less often, Amazon Nova 2 Sonic or Flux → GPT-4.1 → ElevenLabs Flash?

Flux → GPT-4.1 → ElevenLabs Flash, by 0.4 points. The agent went silent for 10 seconds or more on 1.2% of Amazon Nova 2 Sonic calls and 0.8% of Flux → GPT-4.1 → ElevenLabs Flash calls.

Which is cheaper, Amazon Nova 2 Sonic or Flux → GPT-4.1 → ElevenLabs Flash?

There is no verified per-minute rate for Amazon Nova 2 Sonic and Flux → GPT-4.1 → ElevenLabs Flash, so cost cannot be compared yet.

Where does the Amazon Nova 2 Sonic vs Flux → GPT-4.1 → ElevenLabs Flash 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. The cascade runs the same agent for reference and is never ranked.