The rumors are true! Legendary pokemon are officially coming to Pokemon Go, with developer Niantic announcing their arrival in an official blog post on Thursday morning.

It had been heavily rumored that they would finally release legendary pokemon at Pokemon GO Fest in Chicago this weekend. If the players in Chicago can defeat the first legendary to appear, they will start to appear in raid eggs around the world!

From Niantic:

On July 22, thousands of Trainers in Grant Park for Pokémon GO Fest and the millions of others around the world will be working together to unlock in-game bonuses for the entire Pokémon GO community. If they manage to catch enough Pokémon during the Pokémon GO Fest Challenge Windows, the first Legendary Pokémon will be revealed in Grant Park. If the Trainers in Chicago succeed in defeating the Legendary Pokémon, that Pokémon will start appearing in Raid Battles around the world, after Pokémon GO Fest.

The release trailer shows the Generation I legendary birds (Zapdos, Articuno, and Moltres) and at least one from Gen II (Lugia). There was no sign of Mew or Mewtwo (I lied, he shows up briefly at the end), or the Gen II legendary beasts (Raikou, Entei, and Suicune).

In the interest of balance, legendary pokemon will not be allowed to defend gyms, although they can be used to battle gyms of opposing teams and defeat tough raid bosses.