Robert Downey Jr. was the only member of the Avengers: Endgame cast who was allowed to read the entire script. Marvel Studios is legendary for keeping their secrets under wraps, which often involves not handing out full scripts to the cast or even handing out scripts with fake endings in them. Endgame is on the way and a lot of the cast members aren't even sure how everything will end, but when RDJ says the last 8 minutes of the movie are the best thing in the entire Marvel Cinematic Universe, you might want to believe him.
In a new interview, the Russo Brothers reveal Robert Downey Jr. was the only one to get a full Avengers: Endgame script, though they believe Chris Evans might have too. However, they can only vouch for RDJ at the moment, which makes sense. He's the guy who helped bring the MCU to where it is today and was the first one out of the gate. With that being said, this could very well mark the last time we see RDJ as Tony Stark on the big screen, though that has not been confirmed at the moment.
Tom Holland and Mark Ruffalo definitely were not given any portions of the script except for their lines. When Ruffalo was doing Infinity War, the directors had him shoot different endings, including a death scene. The actor didn't even know if the Hulk survived until he witnessed the movie at the premiere. Holland admits that it's hard to shoot with the Russos because he often times doesn't know who he's fighting because they're worried he'll leak something out. Thankfully for the Russo Brothers, Tom Holland has been sitting the Avengers: Endgame promotional tour out.
Chris Evans has admitted to seeing the first half of Avengers: Endgame, but he has not said anything about reading the entire script. The Russo Brothers may have just opened a big can of worms by revealing Robert Downey Jr. and possibly Chris Evans were able to read the entire Endgame script ahead of anyone else. One could imagine Scarlett Johansson being able to throw some weight around to get in on the script too, but what if the Russos didn't let her or Chris Hemsworth? There could be some fights amongst Earth's Mightiest Heroes and their directors in the near future.
Obviously, the less people who know about how Avengers: Endgame pans out, the better it is for everybody. The cast, Scarlett Johansson specifically, have stated how hard it is to keep everything a secret and admitted to getting a form of PTSD from keeping everything hidden. While Johansson is clearly exaggerating, it is truly some pressure that some are better at keeping inside than others. The Russo Brothers are masters and you can check out the interview with them below, thanks to the Rotten Tomatoes YouTube channel.