https://www.polygon.com/2018/10/16/17984626/pokemon-go-gen-4-region-exclusives-sinnoh

The fourth generation of Pokémon has started to appear in Pokémon Go, which means there’s a reason to go out into the wild again. Just don’t expect to be able to catch everything currently available from the Sinnoh region without some traveling, because there are already new region-exclusive Pokémon in the wild.

The Silph Road community is crowdsourcing data on which gen-four Pokémon players have found and where, and three stand out as the rarest thus far. Carnivine, Chatot and Pachirisu — inspired by a Venus flytrap, a talking parakeet and a squirrel, respectively — can only be found in specific areas worldwide, according to early reports.