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.
The small model of Pipecat's second PhoneLLM release, open weights.
| Scope | pass^5 | pass@1 | E / M / H | Tools | Handoff | Final DB | TTFT | Cost/hr |
|---|---|---|---|---|---|---|---|---|
| Cross-industry | 13.3% | 25.1% | 54 / 17 / 19 | 25.3% | 62.9% | 51.6% | 224ms | $0.055 |
| Healthcare | 13.3% | 25.7% | 70 / 21 / 8 | 25.7% | 65.0% | 64.0% | 227ms | $0.064 |
| Legal | 3.3% | 11.0% | 10 / 9 / 13 | 11.0% | 58.3% | 19.7% | 225ms | $0.042 |
| Customer support | 23.3% | 38.7% | 82 / 21 / 35 | 39.3% | 65.3% | 71.0% | 220ms | $0.059 |
E / M / H is pass@1 on easy, medium, and hard tasks. Gate columns are the share of conversations that cleared each check.