NC-Bench: An LLM Benchmark for Evaluating Conversational Competence

Existing LLM benchmarks evaluate what models say, such as whether answers are correct, faithful, or helpful, but they do not test whether models produce the right type of conversational action at the right point in an interaction. The Natural Conversation Benchmark (NC-Bench) fills this gap by evaluating conversational competence: the ability to perform structurally appropriate actions such as repairing, closing, or refusing, as defined by conversation science. Grounded in the Natural Conversation Framework (NCF), NC-Bench comprises three sets: (1) the basic set evaluates fundamental sequence management practices, such as answering inquiries, repairing responses, and closing conversational pairs; (2) the retrieval-augmented generation (RAG) set applies the same patterns but incorporates information-seeking via RAG; (3) the complex request set extends to requests involving more intricate sequence management. Each set tests a model's ability to produce contextually appropriate conversational actions in response to characteristic interaction patterns. Evaluations across six open-source models and one closed-source model on 14 interaction patterns reveal quantifiable shortcomings in conversational competence present in current models. By operationalizing fundamental principles of human conversation, NC-Bench provides a lightweight, extensible, and theory-grounded framework for identifying specific conversational action gaps in LLMs beyond topical or task-specific benchmarks.