We don't know. The Absolute HQ is either the finale of act one or the beginning of act two.
The Absolute HQ is finale of act one but! Only if you're on a boat, and there are two other passages that aren't in the underdark. And this way doesn't say "end of first act/ early access", it says "not available in early access", at least in my language. The end of the first act is confirmed by the cutscene on the boat, which sums up all the results of the first act (your decisions and relationships with your companions).