https://www.gamespot.com/articles/pokemon-go-teases-gen-4-pokemon/1100-6460389/

Niantic's popular mobile game Pokemon Go turned two this month, and the developer is celebrating the milestone in a few notable ways. On top of the ongoing summer style Pikachu event, the studio shared a new piece of art to commemorate Pokemon Go's second anniversary, and it contains the first hints that a new generation of Pokemon is on the way.

The artwork, which you can see below, features the trainers and other human characters from Pokemon Go surrounded by many Pokemon that have appeared in the game to date, including several Gen 3 Pokemon and Alolan forms. Intriguingly, among the Pokemon are Turtwig, Chimchar, and Piplup, the starting trio from the series' fourth generation titles, Pokemon Diamond and Pearl.