The Rasterio 1.0rc4 source distribution and wheels for macos 10.9 (or greater) and manylinux1 platforms are on PyPI now: https://pypi.org/project/rasterio/1.0rc4/.
Please remember that
pip install -U rasterio
will install Rasterio 0.36, the last "stable" release, and that you need to execute either
pip install rasterio==1.0rc4
pip install -U --pre rasterio
to get the latest pre-release. Packages for the Anaconda platform (Linux, OS X, and Windows) should be available in the conda-forge channel (under the "dev" label) very soon.
The final 1.0.0 release is now tentatively scheduled for Tuesday, July 12.