Sure, Google's monorepo uses *Piper* (an unreleased Perforce-alike they
made in-house) not git, which can scale to 25,000 committers in a single
trunk (they have been doing trunk-based-development complete with a
PR-alike workflow since the mid 2000's).
They also use Blaze as a build system (partially released to OSS-land as
Blaze) which is a directed graph build system rather than a (depth-first)
recursive one like Maven.
Those two differences didn't stop Tim Krüger from taking is colleagues into
the mono-repo world with Git and Maven as factors, and implement the same
expand/contract capability that Google has.
Paul Hammant DevOps <https://devops.paulhammant.com/> Let me give you a
step by step plan to get out of the hell of ClearCase and crazy branching
models and into the world of high-throughput CD on DevOps foundations.