Yes it's today. But "don't play on patch day" is still applicable!
Download size for PS4 is 11.011GB (ref)
The Xbox update is 8.99gb.
Just started it up and wow, everything looks much more crispier and detailed.
Lots of qol updates, scanning creatures is much easier now.
It's only a first impression but I'm very excited already.
HG realy did some fine work on this update, no bugs found so far.