This article considers the problems of forecasting 100 h long-term rupture strength of sheets and rods made of α-, pseudo α-, and α + β- titanium alloys at 200–600 °С. Through the generalization of publications, the authors analyze temperature dependencies in the long-term rupture strength of annealed semi-finished products made of titanium alloys of various classes. They compare the long-term and short-term rupture strength limits at operating temperatures. The authors develop models for the theoretical rationale of the 100 h long-term rupture strength limit of titanium alloys at temperatures of 500–550 °С based on the results of short-term mechanical tensile tests.