The microstructure, mechanical properties, and thermal stability of arc evaporated Ti_1-x-yAl_xTa_yN hard coatings were systematically investigated by varying the Ta content in the range of 0<y<0.231. A combination of differential scanning calorimetry and vacuum annealing up to 1500°C with subsequent x-ray diffraction analysis and nanoindentation measurements provided comprehensive insight into the microstructural evolution of the coatings and the resulting impact on their mechanical properties. With the addition of Ta to the metastable Ti_1-xAl_xN solid solution, spinodal decomposition and wurtzite phase formation are shifted to higher temperatures. Consequently,the temperature range where Ta-alloyed coatings maintain their hardness is extended up to 1000°C.