I've announced the move elsewhere, but have been late to mention it here. Rasterio has been transferred from https://github.com/mapbox to https://github.com/rasterio. Today I transferred the affine project, which rasterio depends on, from my own personal repos to the same rasterio org.
Before I left Mapbox, about 45% of the project's commits were authored by folks outside the company. Now, that number is closer to 90%. Moving the project keeps the code open and accessible to its developers and makes it easier to maintain. Making the case for the move at work was pretty easy. Teams at Mapbox that use rasterio want bug fixes and new releases. The Platform team has one less oddball CI configuration to support. I'm grateful for the attention and help of Mapbox's Legal and IT teams during a busy, busy time. It was fun to work with these folks on one last project.
I'm planning to stay very involved in these projects. Go and try the new 1.3 pre-release and report back if you find any new bugs.