Christopher Markus & Stephen McFeely have written each of the solo Captain America films as well as Thor: The Dark World. After Civil War, which many viewed as Avengers 2.5, their next script hitting movie screens will be Avengers: Infinity War, which was once a two-part film but was recently restructured as separate movies. However, Markus and McFeely told Yahoo! Movies that they're working on both scripts in tandem.
"We're many drafts in. We're on the third draft of movie one and the second draft of movie two. [We're writing them in tandem] as much as we can. On any given day, you're only working on one but that doesn't mean that next week, you aren't working on the other one. And certainly, notes are coming in and all sorts of production stuff is coming in, like for instance, 'that thing over there is now a window not a door so adjust that.' Or, 'we're not going to this town now, we're going to this town.' That kind of stuff happens constantly and will continue to happen for the next few months. "
"When we lock ourselves in a room with the Russo brothers and a couple of execs from Marvel, one wall has cards for movie one and the other wall has cards for movie two and another wall has little baseball cards of every character still alive in the Marvel universe - down to Darcy's boyfriend in Thor 2 - literally, anybody who did not die and has been established as alive. And then we looked at that began to shuffle the cards around. So basically, the big scene is when Darcy's boyfriend and Galactus get together and....[laughs]. "
They later clarified that the bit about Galactus was just a joke so don't fire up those speculation engines. Although depending on what 20th Century Fox does with the Fantastic Four following its second attempt to lauch a franchise, the day when Galactus is appears in the MCU might not be too far off.
Avengers: Infinity War will arrive in theaters on May 4, 2018.