Full specs posted on Eurogamer and I'm sure many other places.
Mostly stuff we already knew, but the removable expansion thing is something they haven't talked about until now. I get why it's necessary in order to enable the required I/O bandwidth for Series X games, but no longer being able to use any old external drive is a bit of a bummer. The split between backward compatible games optionally stored on slow storage and Series X games on fast storage seems like it's going to get a little annoying.
And I'm sure those expandable storage cards are going to be expensive AF.