Marvel has not officially announced on when the first trailer of the Avengers 4 will released but buzz were rife that November 28 is the trailer launch day and that's why today all the fans of entertainment industry with their bated breath are enthusiastically waiting for it. For those who don’t know the trailer of Avengers 4 was out last year on November 29 which was a Wednesday and speculators claimed that the trailer can release on November 28 and by the way the day is again a Wednesday. Also, today there is a special screening of Avengers: Infinity War and is organized by Collider. 
After the screening, Joe and Anthony Russo will participate in special Q&A session as well and this news has added more fuel to the buzz of teaser coming out today.
But now most recent reports suggested that the first trailer of Avengers 4 will come soon but not today. MCU Cosmic’s Jeremy Conrad, who is one of the well-known leakers took to his Twitter handle  to burst hopes of fans by asserting that the trailer is not releasing this week. 
“Don’t get too hyped up for an Avengers 4 trailer this week. If it happens, that’s great, but as of right now (Monday afternoon) it’s starting to sound doubtful. Fingers crossed that things change and they surprise everyone."