If you want to see the cast of Avengers: Infinity War assemble during the D23 Expo, Disney has released a video of the panel that they held at the event. It features Marvel Studio President Kevin Feige introduced a ton of cast members from the film! Some of those actors include Josh Brolin, Dave Bautista, Tom Holland, Benedict Cumberbatch, Robert Downey Jr., Chris Evans, Mark Ruffalo, Chadwick Bousman, and many, many more.
Unfortunately, they do not show the footage that was screened at the event. They are going to save that for Comic-Con. You can read my detailed description of the footage that was shown here. It was insane!
It was confirmed at the event that Avengers: Infinity War has completed shooting and the untitled Avengers 4 is about to start.