Initially these movies were to be called Avengers: Infinity War with a Part 1 and a Part 2.
Now the second film has the placeholder of Avengers 4 with the subheading speculated to be a potential spoiler.
Also, unlike the first trailer, he is rocking his signature helmet here and it looks like all of the Infinity Stones are present.
We shouldn’t discount the possibility that Thanos will get a full gauntlet before this duology is over, and maybe he’ll bring back his helmet to complete the look.