Grasshopper 1.0 is included with Rhino WIP and will be released with Rhino 6. It is now feature complete and ready for rigorous testing. Please report any problems that you find.
Grasshopper plug-in developers, many plugins will work without change, unless you call into C++ DLLs that link with the Rhino 5 SDK. It is important that you start testing them now.
Existing Grasshopper users, everything should work as expected, including all existing definitions and plug-ins.
New Grasshopper users, most existing tutorials should work.