Version 4 is major redesign of the internal architecture. As such, it is not binary compatible with previous versions. However, most of the concepts remain unchanged, and the new API will look very familiar to 2.x and 3.x users.
The "not binary compatible" will require changes in this library as well as existing testing tools (like scassandra).
From here:
The "not binary compatible" will require changes in this library as well as existing testing tools (like
scassandra).References