Sprites from Pokémon Sun and Moon have been added to the selection screen of Pokémon GO as part of April Fools.

Experience Pokémon GO Like NEVER BEFORE with Brand-New Graphics!

Trainers, We always want to bring you the most immersive graphics experience possible, and we’re excited to share our latest breakthrough with millions of Pokémon GO Trainers around the world. Starting later today, you can be one of the first to experience this all-new graphics engine.

Experience Pokémon GO like never before with cutting-edge 8-BIT GRAPHICS! Registering approximately twice the definition of 4K, the chunky squares of each pixel provide realistic detail and unbelievable definition. Your Pokédex will feel lifelike in ways previously unimagined on any handheld device ever created.

We feel 100% confident in saying that you’ve never seen Pokémon like this in Pokémon GO! We’re looking forward to your feedback on this brand-new feature. Tell us your thoughts on our latest update with #PokemonGO, and be sure to include a picture of your favorite Pokémon!

Source: https://pokemongo.nianticlabs.com/en/post/newgraphicsapr2018/