Abstract. Transforming constraint models is an important task in recent constraint programming systems. User-understandable models are defined during the modeling phase but rewriting or tuning them is mandatory to get solving-efficient models. We propose a new architecture allowing to define bridges between any (modeling or solver) languages and to implement model optimizations. This architecture follows a modeldriven approach where the constraint modeling process is seen as a set of model transformations. Among others, an interesting feature is the definition of transformations as concept-oriented rules, i.e. based on types of model elements where the types are organized into a hierarchy called a metamodel.