Do LLMs Know What to Ask and When? Evaluating Multi-Turn Information Seeking
In multi-turn interactions a user’s task is often underspecified, and a capable model should recognize when its context is insufficient, identify and acquire the missing information, and defer its answer until the acquired information is sufficient to determine the target. We introduce MT-InfoSeek, a controlled evaluation framework that formalizes multi-turn information seeking as solving a k-underspecified constraint satisfaction problem, providing ground truth for which variables a model must query and when it should stop asking and answer. Spanning mathematics, logic, biology, medicine, and general knowledge (5,251 problems and 9,006 task instances across five domains), the benchmark evaluates which variables a model queries, in what order, and how it uses the acquired information. We find that current LLMs detect underspecification but underestimate its degree, query incomplete variable sets, and often stop before the acquired information determines the target. These results show that information seeking dissociates from answer generation and that final accuracy alone does not measure interactive competence.