They also axed the unannounced survival game they were working on, so likely it's a mix of former HR and support personnel that Microsoft now covers with its own staff, and devs that were hired for the survival game, as apparently they were hiring big for that. Mike Yberra(former President of Blizzard) or however his name is spelled got the boot too... though he says its voluntary, the timing, and that he said previously at Blizzcon that he was in it for the long haul suggests he got told "leave or you're fired".
*edit* Been catching up on this a bit:
Ybarra was apparently not popular at Microsoft, so yeah, almost certainly got the silken boot
Survival game team I'm hearing was estimated ~250 people
Overwatch lost a bunch of their narrative and artist and environment type people
D4 art team got hit
Customer Service is reportedly mostly being outsourced