Avengers 4: Every Character Confirmed So Far
9. Captain Marvel
Confirmed By: Set Leaks
We already knew not to expect Brie Larson's Captain Marvel in Infinity War, as she's not going to be making her debut until her own movie, which comes between the third and fourth Avengers films. But, she is definitely going to appear in Avengers 4.
It stands to reason, with her movie coming between the two releases. It has to - in some way - lead into the "final" Avengers movie and that post-credits scene confirmed it.
The first confirmation that she's involved came courtesy of Atlanta Filming on Twitter, who spotted Brie Larson on set (along with Chris Evans), so you can take that as fairly solid indication (the Twitter account is a great and entirely trustworthy source)...