  Understanding each other is the key to success in collaboration. For humans,
attributing mental states to others, the theory of mind, provides the crucial
advantage. We argue for formulating human--AI interaction as a multi-agent
problem, endowing AI with a computational theory of mind to understand and
anticipate the user. To differentiate the approach from previous work, we
introduce a categorisation of user modelling approaches based on the level of
agency learnt in the interaction. We describe our recent work in using nested
multi-agent modelling to formulate user models for multi-armed bandit based
interactive AI systems, including a proof-of-concept user study.
