Up until Ant-Man and The Wasp, Marvel Studios films have traditionally been released a week early in international markets (such as the UK) compared to the US. Avengers: Infinity War was famously moved to April 27th world wide, and it’s been expected that Avengers 4 would arrive on April 26th internationally while following on May 3rd in the US. As of right now, the official US release date is still May 3rd, but here’s something that may give people hope that they’ll move it up again.
IMAX has released their Q2 earnings, and they list all of the IMAX movies coming out in 2019. The date given for Avengers 4 is April:
It’s entirely possible IMAX is listing Avengers 4 as April as that’s when the international release will be and when the world premiere will be. So it’s possible that the date hasn’t been pushed up yet. But if Avengers 4 is going to have an epic conclusion to the past twenty Marvel movies, they could move it up again to preserve spoilers like they did with Infinity War this year.