Once fabricated, structures and devices typically maintain their properties throughout their lifetime. In recent years, various stimuli, including temperature, pressure, and magnetic fields, have been implemented to actively change the mechanical and other physical properties after fabrication. Yet, most such approaches are limited to individual properties, specific geometries, or require high structural complexity. Inspired by this work – and by these challenges – we propose a framework for programmable and thermally reconfigurable multi-material systems. The initial structure is monolithically fabricated via 3D printing and programmed by integrating active materials that can change their mechanical properties from virtually identical to over two orders of magnitude in difference with respect to a passive base material. By varying the temperature, the programmed structure can actively adapt a wide range of mechanical properties and deformation behaviors, including the deformation mode, Poisson’s ratio, and effective relative density. We anticipate the proposed framework to enable significant progress in numerous technological fields, such as aerospace, biomedical, and robotics.