Most of the other interfaces have also changed in one way or another. In some cases, it is just the interface, the calls, and the parameters names that got changed. In others -- it's the default values, the enumerations, and the expected predefined values. Some calls may no longer exist, some were moved to a different interface, and so forth. All in all, it is safe to say that porting an existing VZAgent 3.0.x application to VZAgent 4.0.0 will require some work. Most of the effort will probably go into learning the new API concepts. The actual changes that you will have to make to your existing code should not be massive but it really depends on the complexity and size of your application. We believe that you should be able to keep the majority of your existing code by making modifications where necessary instead of re-writing the entire application from scratch.