This is the first alpha of CuPy v1!
At the moment, the API and the implementation is equivalent to CuPy included in Chainer v1.21.0, while the installation step is slightly different (you need to install cupy package instead of chainer). See our official documentation for the installation procedure.
Note that the development is currently runinng at pfnet/chainer repository. We will work on adding a new feature only included in this independent CuPy code base. We will also catch up with the updates on pfnet/chainer repository, and so feel free to send any issues and patches for CuPy to pfnet/chainer repository.