The longest MCU film to date is last year's Avengers: Infinity War, which clocked in at two hours and 29 minutes. But that is nothing compared with the reported Endgame runtime, a near-endless three hours and two minutes.
According to Marvel president Kevin Feige, whatever the runtime, he feels it will be the "exact right running length." Speaking to Collider earlier this month, Feige said, “I’m telling you this, it’s gonna be perfect. It’s gonna be the exact running time that the movie needs to be.”
He added that, all going well, the movie will feel much shorter. "Every movie should feel like it’s an hour and 45 minutes. Now, some movies can be 90 minutes and feel like they’re four hours. And some movies can be three and a half hours and feel like 90 minutes."