This is according to a report from BGR who points out that the Russo brothers, the director team behind the movies, did state that the trailer will be released by the end of the year. They also point out the fact that tomorrow, the 28th of November, will see an event hosted by Collider where the Avengers: Infinity War movie is expected to be shown again, and that the Russo brothers will be in attendance.
This will give fans a chance to ask the brothers questions about the movie, and as BGR notes, seems like the perfect opportunity (given how many fans will be in attendance) to announce and launch the trailer. Note that Avengers 4 has yet to receive an official title, so it is possible that the trailer could be its official reveal.
Also we’re not sure if this will be the full trailer or if it might only be a teaser, but either way like we said, many can’t wait to find out how this story plays out, so any little bit, even a teaser, will help. Don’t get your hopes up just yet but we’ll keep our eyes peeled and hopefully we’ll have something for you guys tomorrow.