The primary focus of release 4.0 is the complete restructuring of the way models are handled. Models are being pulled out into a separate repo, sasmodels, which can easily be used independently. In the process we are taking the opportunity to bring consistency to the models from naming, parameter naming, documentation and code organization. This will finally make addition or editing of integrated models to be accessible to the average user. This release should also add relatively transparent access to GPU processing using OpenCL which should substantially increase the performance of complex fitting problems.