In either case, it sounds like Favreau plans on making an appearance as Happy in an Avengers movie; whether that happens in Infinity War or Avengers 4 remains to be seen.
Although he’s not allowed to explicitly reveal his involvement, it sounds like Jon Favreau will be making an appearance in Anthony and Joe Russo’s Avengers: Infinity War next year.
It’s also possible, though highly unlikely, that the actor-director could be appearing in Peyton Reed’s upcoming Ant-Man and The Wasp, which also films alongside Avengers in Atlanta.
Interestingly, while the immediate assumption would be that Favreau would be reprising his role for Infinity War, it’s also possible that he’ll be making an appearance in the currently untitled Avengers 4, which is scheduled to enter production this month.