A team of us moved it off Rackspace in 2013, it’s been mostly in a set of GitHub operated colo since then. Used to be there was some workloads on AWS and a bit of DirectConnect. Now it’s some workloads on Azure.
To the best of my knowledge there’s been no Rackspace in the picture since about 2013, the details behind that are fuzzy as it’s been 10+ years since I worked on infrastructure at GitHub.
[1] https://thenewstack.io/github-will-prioritize-migrating-to-a...
Honestly I don't know half the features they have added because the surface is huge at this point everyone seems to be using a (different) subset of them anyway.
So a feature freeze isn't likely to have much impact on me.
EDIT: went and checked - https://github.blog/news-insights/github-is-moving-to-racksp... not sure if they moved again before the MS acquisition though.