670,000 commits. Thats big. But only 2K merges? I assume push straight to master in most cases?

I published an updated extension of this post's linked article in Empirical Software Engineering. You can read it without a paywall at https://rdcu.be/b7FzE. You may also be interested to see the actual GitHub repository at https://github.com/dspinellis/unix-history-repo.

Interesting to see the decisions they took regarding which flavours they chose to include.