"The team is also pursuing an experimental effort with Mercurial an open source DVCS similar to Git. The goal is to add scalability features to the Mercurial client so it can efficiently support a codebase the size of Google's. This would provide Google's developers with an alternative of using popular DVCS-style workflows in conjunction with the central repository. This effort is in collaboration with the open source Mercurial community, including contributors from other companies that value the monolithic source model."
Not sure why I got heavily downvotes. This above was the pieces of information that got me to think they were all on hg. So judging from the comment I stand corrected.
Your assumption was pretty reasonable based on the public information. Honestly I’d love to talk about how Google does source control/ code review etc. because it’s actually pretty interesting at this point. You know... for some values of interesting.
Here's the money quote:
"The team is also pursuing an experimental effort with Mercurial an open source DVCS similar to Git. The goal is to add scalability features to the Mercurial client so it can efficiently support a codebase the size of Google's. This would provide Google's developers with an alternative of using popular DVCS-style workflows in conjunction with the central repository. This effort is in collaboration with the open source Mercurial community, including contributors from other companies that value the monolithic source model."
Project that forward logically by two years.