Tomorrow is July 28, and from 1 pm EDT on that date until 1 pm EDT on August 1, you will be able to play Rainbow Six Siege for free. The free weekend leads into the release of the Operation Skull Rain expansion, as well as the beginning of the game's third season, both of which are set to go live on August 2.
Ubisoft said in a separate post that season three will be “focused on improving the health of the game.” That means things like implementing the BattleEye anti-cheating system, improving features like the Kill Cam, and fixing dynamic clipping for skinned objects, which “reduces greatly the amount of body parts leaking through walls and shields.”
To get into the action, fire up Uplay and hit the Rainbow Six Siege “Free Weekend” banner. If you don't have Uplay, you can get it here.