The term “modelgen” refers to the device model generator and language that has been part of the Gnucap project from early on. Modelgen reads device descriptions and emits C++ code to be compiled into plugins. Support for Verilog-AMS compact models has been implemented in a modelgen successor, ”modelgen-verilog”, following the design patterns and device architecture. Major technical advantages of the latter are automatic differentiation and support for device specific numerical tolerances. Others will follow by adding subsequent Verilog-AMS features.