Based on the efforts at the first-ever Pokémon GO Fest in Chicago, Illinois, Lugia and Articuno were unlocked. In the weeks ahead, they will be joined by Moltres and Zapdos. The official battle periods for all three Legendaries are as follows:
- Articuno (Team Mystic) released on Saturday, July 22 and available through Monday, July 31.
- Moltres (Team Valor) to be released on Monday, July 31 and available through Monday, August 7.
- Zapdos (Team Instinct) to be released on Monday, August 7 and available through Monday, August 14.
Source: Official Niantic blog