The Rainbow Six: Siege beta will be starting today at around 9am eastern time and Ubisoft have released a new trailer to celebrate. If you want to get involved, head over to the official site and sign up to the waiting list. It looks like they'll be distributed randomly, though a lot of folks have been getting them from various other official sources. That same page is where you need to go if you have a key but haven't redeemed it yet. This is at least partly a stress test, so I wouldn't be surprised if a lot of people are let in eventually.
Ubi already have a post up on the official blog outlining the issues they expect players to face. The matchmaking rate isn't great, averaging about 60% for solo players and only decreasing in parties. Obviously, they're looking to improve, but suggest if you don't find games in 90 seconds or less to restart the process.
As for what you'll get to play with, as and on, they're promising 14 characters - sorry, 'operators' - to play as, each with a unique set of skills. Balancing your team out to be able to counter threats effectively will be vital. There will be a pair of PvP modes based around attack and defense, one protecting a bilogical agent that must be captured and the other preventing bombs from being defused. Tomorrow a co-op PvE mode will unlock that lets teams of players take on AI and try to better scores and times. You'll be playing these out on three maps, all of which have day and night modes. There's the house map from the original trailer, a consulate and the home base of Team Rainbow.
There's already a bunch of people streaming the technical test that was previously NDA'd, if you can't wait. Ubisoft also did their own livestream yesterday. We'll be jumping into the beta and providing some Team PCGN thoughts in the near future.