Update: October 5, 2018
Rumor: Avengers 4 Possibly Titled AVENGERS: ANNIHILATION
The latest rumor originates with
MCUCosmic, who claims a reliable source has revealed the title to him. According to the site, the movie will be called
Avengers: Annihilation. This idea is derived from a classic comic book story from 2006, written by Keith Giffen. While the plot of
Avengers 4 isn't expected to be anything like the
Annihilation arc,
MCUCosmic is right to point out that the MCU plays fast and loose with its comic book inspirations. After all, in the comics,
Avengers: Age of Ultron was a time-travel story.
But this particular rumor doesn't seem particularly credible.
MCUCosmic has a mixed reputation in terms of the accuracy of his "scoops," and, as a result, this should be taken with a serious pinch of salt. Indeed, when it comes to major scoops like this, it's usually best to have at least three independent sources verifying them. They admit they only has the one.
https://screenrant.com/avengers-4-title-annihilation-rumor/