Concrete details on Avengers: Infinity War and the unnamed Avengers 4 haven't been revealed to the public, as of this writing. Though fans know the basic essentials - the Avengers team with the Guardians of the Galaxy to fight Thanos - everything else surrounding them has been a big guessing game, especially with no trailer in sight. However, the latest set photos for the fourth Avengers film might be hinting at something interesting involving Iron Man.
The latest set photos show Robert Downey Jr don some clothes that will be very familiar to MCU fans. One photo has Downey Jr in SHIELD swat gear talking to Ruffalo in a motion capture suit, hinting at a flashback between Tony Stark and The Hulk. We also see another photo with the character wearing his Black Sabbath shirt, which he wore during the very first Avengers movie.
Iron Man has always been an integral part of the MCU, so it makes sense to give him a big role in these Avengers films, whatever it may be. Stark did get a vision from Scarlet Witch in Age of Ultron about a possible alien invasion, which will be coming true in these Avengers movies. Only time will tell if they play an integral part to these flashback sequences, assuming that's what they are.
Avengers: Infinity War is slated for a May 4, 2018, release. The unnamed Avengers 4 comes out on May 3, 2019.