Niantic Labs says the Time Travel Pokémon will be available through the new task that will be made public on Aug 20.
“Complete tasks to gain XP (experience), receive useful items, and even encounter certain Pokémon on your journey!” it says on its website.
Niantic Labs released another mythical Pokemon, Mew, in a similar fashion in March, as a reward for ardent players that completed a series of increasingly complicated tasks.
The company assures that players can start doing the Celebi-related tasks as long as they've done the first three in the series of Mew-related tasks.
As with the Mew quest, there is no deadline set, allowing players to complete both at their own pace.
Players who attended the Pokémon GO Fest 2018 in July would have already unlocked Celebi, though they can do the tasks a second time and be rewarded with candy, used to power up the Pokemon.
Another perk of the quest is the appearance of more Pokemon from the Johto region plus daily research tasks relating to them.
This is potentially a draw for new players who might not have had a chance to catch Pokemon from the Johto region, which are harder to find among those available from all regions.
Niantic Labs also announced a new way to log in to the game, called Niantic Kids, powered by SuperAwesome, a child friendly log-in platform.
With Niantic Kids, parents will be able to manage their child’s privacy, allowing them to review and approve their child’s permissions before they can play and provides options to control the personal information shared in Pokémon GO.