At a special screening of Black Panther on Thursday evening, Sirius XM journalist Erick Weber posted a tweet of responses from Marvel Studios’ Kevin Feige on when the Avengers 4 trailer will debut, among other questions.
Feige said the trailer will be released “before the end of the year,” which confirms the Avengers 4 trailer will debut within approximately 2 months – sometime in 2018.
Source: IGN.com Marvel Studios Boss Kevin Feige on When the Avengers 4 Trailer Will Debut and Guardians 3 Status