What does Facebook use internally these days. I'm amazed that the state of review tools is still at or behind what we had a decade ago for the most part.

It’s still phabricator

Any idea if their internal version has improved dramatically since they stopped maintaining the public version?

I don't think they ever maintained the public project. Priestly spun off a company to do that.

It has improved massively by 2023 when I left.