Niantic has announced that Celebi will be available in Pokemon Go for players worldwide beginning on August 20.
As announced on Pokemon Go’s official site, Celebi will become available in Special Research and can be accessed after a player has completed step three during the Mew Special Research quest.
Players will be able to complete tasks from the Mew or Celebi line of Special Research simultaneously without having to abandon one or the other.
Celebi was previously released to players who attended Pokemon Go Fest in Chicago. Those players will not be able to earn a second Celebi from this new set of research, but will instead receive “a new bounty of Candy to power up your Celebi.”
Source: IGN.com Pokemon Go: Celebi Special Research Worldwide Release Announced