E3 begins today with the Xbox E3 Briefing at Microsoft Theater in LA, scheduled to livestream later today.
Microsoft has a lot to show this year, some of which it has already revealed; Xbox Game Pass for PC is coming, Gears 5 and Age of Empires' Definitive Edition are confirmed to be coming to Steam, and we can surely expect to see more details about xCloud.
There have been an unfortunate amount of leaks over the past few weeks, but we should still expect to see plenty of surprises and new announcements. If not for those, it would perhaps be a good idea to watch for certain other incentives.
Microsoft's event is expected to be about two hour long, starting at 1pm PT / 4pm ET / 10pm CEST. You can watch it on Mixer for the probability of winning something, or on YouTube (embedded below), or Twitch. Mixer stream is also in 4K.