Pokemon Go is swapping out Zapdos for Articuno as a Research Breakthrough reward starting on June 1st.
Earlier this year, Pokemon Go added a new daily quest feature called "Field Research," in which players completed tasks ranging from capturing a specific species of Pokemon to spinning a certain number of PokeStops in exchange for in-game rewards like XP, items, or Stardust.
For each day that a player completes a Field Research task, they earn a stamp that indicates their progress to completing a "Research Breakthrough" - a bundle of prizes that include rarer items and a capture encounter with a Legendary Pokemon.
Starting on June 1st, Articuno will be the big Research Breakthrough prize, available at a low level whenever players complete Field Research tasks on seven different days. Articuno hasn't appeared in Pokemon Go in months, so this is a great way for players who started the game late or missed out on last summer's Legendary festivities to add this Pokemon to their PokeDex.
Adding Legendary Pokemon as a Field Research reward was a great way for Pokemon Go to help out those players who can't or won't participate in Raid Battles. While you previously needed a group of 4 or more Pokemon Go players to beat a Pokemon like Articuno, any player can capture Articuno after hitting the Research Breakthrough milestone. Plus, players can use Ultra Balls to capture Articuno and have a hypothetically unlimited number of chances to capture the Legendary Pokemon, which are both big upgrades over the Raid Battle capture encounters.
As with Moltres and Zapdos, Articuno will only be available as a Research Breakthough reward for one month. It's unclear whether Pokemon Go will switch to Lugia or Ho-Oh as July's Research Breakthrough reward, or if they'll switch to one of the Legendary Beasts (Suicune, Entei, and Raikou.)
In addition to switching up the Research Breakthrough rewards, Pokemon Go will also add several new Field Research tasks focused on Water-Type Pokemon. This follows last month's emphasis on Electric-Type Pokemon in conjunction with Zapdos's arrival as a Research Breakthrough reward.
Pokemon Go is also set to add Alolan Forms to the game as a way to celebrate the summer. While these Pokemon aren't technically "new" Pokemon, their new forms means more new attacks, strange new typings, and of course more Pokemon to capture and add to a player's collection. Pokemon Go has not announced a launch date for the Alolan forms, but they are expected relatively soon.