The cover of the latest issue of Japanese magazine CoroCoro Ichiban has been revealed and features what appears to be Gigantamax forms for Eevee, Pikachu, Meowth and Charizard:
There is also an official announcement coming later today at 1pm UTC (6am PT/9am ET/2pm BST) which may feature details of these Pokémon. We'll bring you the news when it happens.