> They store complete version history with each keystroke of a document.

I would expect them to only store a diff between each version instead of storing the whole thing. Couldn't find much about this after a quick search.

They don't store a complete version history. It just uses checkpoints in their timeline of real-time edits and computes the differences when you need them. Those deltas can also be compressed.

It's naive to think they don't compress.