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.
Pipecat's open-weights phone-agent LLM: a full fine-tune of NVIDIA Nemotron 3 Nano 30B-A3B (3.5B active parameters, 256K context).
| Scope | pass^5 | pass@1 | E / M / H | Tools | Handoff | Final DB | TTFT | Cost/hr |
|---|---|---|---|---|---|---|---|---|
| Cross-industry | 10.0% | 19.1% | 52 / 11 / 11 | 19.5% | 60.7% | 46.3% | 394ms | $0.095 |
| Healthcare | 15.0% | 19.0% | 80 / 7 / 1 | 19.0% | 57.7% | 54.0% | 394ms | $0.093 |
| Legal | 1.7% | 10.7% | 10 / 5 / 17 | 10.7% | 54.3% | 19.0% | 399ms | $0.090 |
| Customer support | 13.3% | 27.7% | 65 / 20 / 17 | 28.7% | 70.0% | 66.0% | 394ms | $0.102 |
E / M / H is pass@1 on easy, medium, and hard tasks. Gate columns are the share of conversations that cleared each check.