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 non-reasoning GPT-4.1, the default LLM in many production voice-agent stacks.
| Scope | pass^5 | pass@1 | E / M / H | Tools | Handoff | Final DB | TTFT | Cost/hr |
|---|---|---|---|---|---|---|---|---|
| Cross-industry | 41.7% | 71.3% | 89 / 73 / 61 | 72.6% | 86.9% | 86.0% | 693ms | $0.894 |
| Healthcare | 40.0% | 64.3% | 98 / 73 / 39 | 64.7% | 84.3% | 87.7% | 666ms | $0.934 |
| Legal | 33.3% | 75.7% | 68 / 82 / 73 | 76.3% | 94.7% | 83.3% | 640ms | $0.799 |
| Customer support | 51.7% | 74.0% | 100 / 64 / 71 | 76.7% | 81.7% | 87.0% | 778ms | $0.949 |
E / M / H is pass@1 on easy, medium, and hard tasks. Gate columns are the share of conversations that cleared each check.