For a number of creep resistant steels, the creep ductiliy decreases with increasing temperature and time. As a function of stress, the ductiity is often describe with an S-shaped curve with an upper and a lower shelf level. As a function of time, the S-shape is inverted. If the ductility is high, the rupture is referred to as ductile, and for low ductility levels as brittle. Ductile rupture is believed to be due to a plastic instability such as necking. Brittle rupture on the other hand is controlled by the nucleation, growth and linkage of creep cavities. With the help of the basic models for creep deformation and cavitation, the rupture stress and ductility can be predicted. Several models exist for the influence of multiaxiality on the creep ductility. Although the models are based on different principles, they predict approximately the same behavior, which is verified by comparison to rupture data for notched bars.