The Open System for Earthquake Engineering Simulation (OpenSees) analysis engine for both linear and non-linear analysis of structures can be used in several CYPE programs.

The use of this analysis engine, developed by Frank McKenna, Gregory L. Fenves and Filip C. Filippou at the University of California at Berkeley, is widespread all over the world and is highly regarded as a reference analysis engine among academics and professional experts in advanced structural design. Furthermore, its use for simulating the behaviour of structural and geotechnical systems subjected to earthquakes, as indicated by its name (Open System for Earthquake Engineering Simulation), is also widespread.

To use "OpenSees. Professional version" in the analysis programs for which it is available, the user license must include the corresponding permission.