Last week Saturday I happened to come across the title for Avengers 4, which I was told was Avengers: Endgame.
Note: This was before the Monday premiere of The Avengers: Infinity War.
I then proceeded to run a poll on our social media questioning if I should release the title (to build up a little hype).
Thursday afternoon I posted the Avengers: Endgame reveal and stated to consider it a rumor at the time.
I can now say with 100% certainty that Avengers: Endgame is the title for Avengers 4 (well, assuming they don't change it now).
I have been provided further information on Avengers: Endgame and the original source of the information.
It is someone who does work for Disney. I know his/her name and job title, and, of course, I shall say no more and won't reveal the person's identity.
Slight spoiler follows for The Avengers: Infinity War.
You will also note that I revealed Avengers: Endgame as the title for Avengers 4 prior to the release of Infinity War, and then during Infinity War, Doctor Strange drops the title while talking to Tony Stark.
The title definitely fits with what is to come, as the sequel is indeed "bigger" and "better," just like the writers said.
I'll also add a little tease in that Marvel's true endgame is what comes next.