Johto’s three Legendary Pokémon Raikou, Entei, and Suicune are now available in Pokémon GO. From now until September 30th, the Electric-type Raikou will be available in the Americas, whereas the Fire-type Entei will be available in Europe and Africa and the Water-type Suicune will be available “throughout the Asia-Pacific region.” On September 30th, they will move to a new location. On October 31st, they will move to the last location that they have yet to visit. Once they have visited all three locations, they will no longer be available to fight.
Niantic also announced that it will be field testing the “EX Raid Battle” system in “select regions around the world” beginning September 6th. These battles will be similar to normal Raid Battles, but will be exclusive to “trainers who have successfully completed a Raid Battle at the Gym where the EX Raid Battle is taking place.” Those who are invited to take part will be sent “EX Raid Passes […] soon.”
You can find the full announcement here.