The codebase in GitHub is pretty much exactly the same as the internal, the main exceptions being things like having to rewrite include paths for files, filesystem plugins for internal cluster filesystems, etc; and those things are modularized so that we can have equivalent implementations in the OSS build to support things like HDFS and GCS filesystems, RDMA network layer communication, etc.

We daily sync the code between the two repositories using a suite of tools we've built. I'm on sync rotation this week and you can see all of my commits and activity on GitHub as proof; I merged something like 60 commits from the community just this week. It wouldn't make any sense for anybody (Google or the community) to maintain two different versions for something that is actively being developed by so many contributors. I've also directly worked with NVidia engineers on improvements they've made (and merged) to the system; the ones I've dealt with are great, so that statement is also false.

I'll be giving a talk about all the work we do to make this possible at OSCON next week, and if you are there feel free to catch me to ask me questions.