Last year Marvel Studios revealed that Avengers: Infinity War Part 1 & 2 would be two completely different films with Part 1 & 2 being dropped. They also revealed that the two films will be shot co-currently. Which means one day they will film one film then the next they would film the other film. This would span a full 11-month shoot starting from this past January until October.
However, during the premiere of Guardians of the Galaxy Vol 2. Marvel Head Kevin Feige revealed to Collider that the films will instead be shot back-to-back like originally planned:
“We’re doing them one right after another… It became too complicated to cross-board them like that, and we found ourselves—again, something would always pay the price. We wanted to be able to focus and shoot one movie and then focus and shoot another movie.”
Avengers: Infinity War hits May 2018 and Avengers 4 hits May 2019