This paper discusses the use of chalcogenide phase change materials to create tunable metamaterials as potential candidates for application to adaptive coded aperture control in the infrared. Phase change materials exhibit large and reversible changes in optical properties (Δn, Δk) when switched between the amorphous and crystalline phases. Thermally-induced phase transitions from the insulating amorphous to the conductive crystalline state can be controlled through external means, facilitating the design of reconfigurable metamaterial devices that operate with ultrafast response times. In this work, robust global stochastic optimization algorithms were combined with full-wave electromagnetic simulation tools to design periodic subwavelength chalcogenide nanostructured arrays to meet the specified device performance goals in each phase. The measured optical properties (n, k) of deposited chalcogenide thin films and nanofabrication constraints were incorporated into the optimization algorithm to guarantee that the designed nanostructures could be manufactured. By choosing the appropriate cost functions, adaptive metamaterials were designed to switch between transmissive and reflective, transmissive and absorptive, and reflective and absorptive states. These design demonstrations represent a significant step forward in the development of adaptive infrared metamaterials.