Robert Downey Jr. confirms his return as Tony Stark, aka Iron Man, in Anthony and Joe Russo’s untitled Avengers 4 movie.
While that may very well happen in Infinity War, that doesn’t preclude Downey Jr. from returning for Avengers 4.
What’s more, the photo also expressly confirms Paul Rudd’s addition, making Avengers 4 his first Avengers movie (he and Evangeline Lilly aren’t confirmed to appear in Avengers: Infinity War).
However, that doesn’t mean Avengers 4 won’t contain repercussions from Avengers: Infinity War.