Presumably all the internal research and evaluation work. I imagine for each released model they have uncountable unreleased ones.

I would guess a huge chunk of it is for internal testing/experimentation/model development.

They're starting to do things like spinning up wet labs for testing purposes, which requires a lot of hardware interfacing (hence that protocol they announced) and code.

It wouldn't shock me if the bulk of this code was for things typical users don't see.

Exactly. Commit counts are no better than line counts as a software development metric. Where is the actual software?

make smarter models?