Pokémon Go is concluding its current event season with the “Go Fest: Max Finale” on August 23-24. The event, themed around the story climax of Pokémon Sword and Shield, will feature a “Crowned Forme” Zacian and Zamazenta raid battle. A unique Gigantamax Raid battle against Eternatus, available for use by Zacian and Zamazenta, is also part of the festivities.
All 13 released Gigantamax Pokémon in Go will be available during the weekend event, including Butterfree, which debuts as a Gigantamax on August 3. The “Dark Skies” event will run from August 18 to August 24, and trainers can obtain a special “Go Pass: Max Finale” starting Monday at 10am.
Source: https://www.nintendoworldreport.com/news/71791/pokemon-go-announces-dark-skies-event-and-go-fest-max-finale-details