Working paper / 2026
Conversational AI LLM Bench
Abstract
We define conversational AI LLMs as the language models at the center of cascaded voice pipelines, between speech recognition and speech synthesis, that return a first token within one second: a median time to first token of 1,000 ms or less. The Conversational AI LLM Bench (CALLM) benchmarks this category. Each model operates every agent of a multi-agent front desk in healthcare, legal, and customer support, with production-length prompts, executable tools, and per-call database state. A simulated caller pursues a locked task over a simulated phone line, so the model receives only what a speech recognizer would have transcribed, errors included. A deterministic verifier scores tool calls, handoffs, and final database state; pass@1 and pass5 measure single-attempt capability and five-attempt reliability.
Clone the repository, point a model at an industry pack, and reproduce the evaluation environment.
OpenAI's GPT-4o, the earlier flagship that many voice-agent stacks were built on.
| Scope | pass^5 | pass@1 | E / M / H | Tools | Handoff | Final DB | TTFT | Cost/hr |
|---|---|---|---|---|---|---|---|---|
| Cross-industry | 33.3% | 62.3% | 87 / 63 / 49 | 63.7% | 91.2% | 81.7% | 660ms | $1.85 |
| Healthcare | 30.0% | 51.7% | 95 / 54 / 28 | 52.0% | 88.7% | 83.3% | 652ms | $1.94 |
| Legal | 21.7% | 67.0% | 77 / 69 / 60 | 67.7% | 95.7% | 73.7% | 636ms | $1.53 |
| Customer support | 48.3% | 68.3% | 88 / 67 / 60 | 71.3% | 89.3% | 88.0% | 693ms | $2.08 |
E / M / H is pass@1 on easy, medium, and hard tasks. Gate columns are the share of conversations that cleared each check.