Yeah they have jobs up for like 150 positions now and they had been hiring a lot of senior position through the earlier parts of this year and their new studio they bought is supposed to be up and running and fully staffed up by December 2018 from what we heard late last year. The rumour of a 3rd team creating a new IP are interesting but would seem a big ask to staff up fully 2 AAA teams at once. I mean I'd love to believe that artwork we saw from them that looked like Berserk is the 3rd project but that's a long shot indeed. :)
It's not only Playground that are recruiting it's pretty much all MS studios new and old.
We have Rare closing in on 100 strong staff for the new IP they have been incubating whilst they also recruited more staff for a 4th Sea of Thieves content team.
Compulsion Games said they are recruiting for a bunch of positions very soon. Not sure what kind of scope these guys will go for or if they will have multiple teams as most of We Happy Few was developed with 15-20 staff and by the end of it they were 40 strong. I could definitely see them with two teams of around 40 to hit that creative AA space.
The Coalition have staffed up an whole lot since Gears 4 launched and Will likely have a full strength 2nd team going into next gen. Infact I wouldn't be surprised if they are the ones on Perfect dark or at least got 100 staff in collaboration with another studio on the project.
Ninja Theory are staffing up a bunch more also and it sounds like they could end up with 3 teams of 40-60 staff each.
The Initiative are still very small in numbers if led to believe they are still in single digits but are likely to end up 200-300 strong through 2019 with the scope they are building them for.
Undead Labs - Not sure on these but I imagine the next State of Decay will require a lot more staff to hit the AAA mark they always wanted than the 40 that did most of SoD2 which they built up to 60 towards the end of it's development cycle.
Turn 10 Use a lot of contract work but it's possible they grow in numbers to not only do Forza and have a 2nd team but no clue on that and 343 just always seem to be growing at 500+ now but they do more then just game development with all everything Halo ran through them.