Nickel based single crystal super alloys are widely used as aircraft engine blades and are still in the process of development to improve the high temperature capabilities. The typical microstructure of these alloys consists of gamma phase as the matrix strengthened by the gamma prime precipitates. In recent times, addition of refractory metals like Re are tried to improve the creep strength. The first generation of these alloys does not contain any such additions. The second generation of the alloys contains around 3–6% Re. These additions and modifications have been found to improve the temperature capability of the CMSX, though there are limitations in their addition. In this article the microstructural developments, the metallurgical and high temperature behavior of the first and second generation NiSX family subjected to stress annealing, are discussed from engineering point of view. Based on experimental findings reported in literature, deformation maps illustrating the different mechanisms over a wide range of temperature and stress levels for the first and second generation alloys are presented. © 2017, The Indian Institute of Metals - IIM.