A new generation of sensor rich, massively distributed, autonomous systems is being developed that has the potential for unprecedented performance, such as networks of smart buildings, reconfigurable factories, spacecraft constellations and remote earth ecosystem monitoring. To achieve high performance these immobile robots will need to use their sensors to accurately model themselves and their environment on a grand scale. They will use these models to reconfigure themselves dramatically if they are to survive decades of autonomous operations. To be economically viable they will need to be programmable purely through high level compositional models. Self modeling, self configuration, deliberated reactions and compositional, model-based programming are the four key elements of a {\em model-based autonomous systems} architecture that is taking us into the New Millenium.