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Working paper / 2026

CALLM

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.

GitHub repository ↗

Clone the repository, point a model at an industry pack, and reproduce the evaluation environment.

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Qwen3.5 9B

#29 of 29

Alibaba's small dense open-weights Qwen3.5 model, thinking off.

Provider
Alibaba
Model id
Qwen/Qwen3.5-9B
Availability
Open weights
Source
Provider announcement ↗

Results

Scopepass^5pass@1E / M / HToolsHandoffFinal DBTTFTCost/hr
Cross-industry7.2%24.5%54 / 19 / 1625.0%61.0%57.9%410ms$0.100
Healthcare8.3%27.7%65 / 29 / 827.7%63.3%74.0%421ms$0.109
Legal1.7%18.0%25 / 17 / 1618.7%65.7%32.3%391ms$0.091
Customer support11.7%27.7%72 / 10 / 2328.7%54.0%67.3%410ms$0.100

E / M / H is pass@1 on easy, medium, and hard tasks. Gate columns are the share of conversations that cleared each check.