Pokémon GO launched across the globe exactly one year ago and developer Niantic is continuing the game’s one-year anniversary celebration with a special Pikachu wearing Ash’s iconic hat from the Pokémon anime. Here’s the official announcement from the Pokémon GO team at Niantic:
Just a few weeks ago, the one-year anniversary celebration kicked off with a bang. You and millions of other Trainers went outside to battle in revamped Gyms and participate in Raid Battles with family and friends for the first time, but this was only the beginning of an action-packed couple of months. The celebration continues with a special Pikachu wearing a familiar hat appearing all over the world. From July 6 at 1:00 P.M. PDT to July 24 at 1:00 P.M. PDT, Pikachu discovered in the wild will be wearing Ash’s famous hat from the Pokémon animated series, so make sure you don’t miss out on your opportunity to catch one!
Source: Official Pokémon GO blog