Overwatch's Orisa will be off limits to Competitive Play players for a few days after she becomes available.
However, if you were planning on bringing the Guardian bot to Competitive Play right away, you may be disappointed to know that you won't be able to that just yet. Blizzard says that, for one week after release, Orisa will not be accessible in Competitive Play.
The reason for this is that the developer wants everyone to spend enough time with her in casual so that they can learn her abilities and how to best play as or counter her.
This doesn't apply to Quick Play or Arcade mode, where Orisa will be available as soon as the patch goes live. You'll also be able to select Orisa in bot matches.
Orisa releases later today alongside the game's patch 1.9.