Speaking to SFX, the comic book writer said that he's excited for X-Men: Days of Future Past, which will be overseen by First Class director Matthew Vaughn, who also helmed the movie adaptation of Millar's Kick-Ass.
He told SFX: "Vaughn is going for a big sci-fi style thing with X-Men: Days of Future Past."
He also teased the plot of the film, calling it "X-Men meets The Terminator".
"You've got robots, you've got time travel, you've got superheroes - it's got everything in one film," he claimed.
He also said that it is "no spoiler on [his] part" to say that the film goes into an apocalyptic future.
"Cost-wise it's going to go up, and ambitious-wise it's gone up," Millar noted. "But Vaughn can handle it. Vaughn made Kick-Ass for $28 million."
X-Men: Days of Future Past is expected to be released in July 2014.
Watch Michael Fassbender discuss X-Men: Days of Future Past with Digital Spy below: