The new feature is activated with a swipe from the bottom of the chat. Once a message is sent, it will stay on the screen until it is turned off or the app is switched. Of course, users can still screenshot the message before it disappears.
Some users may have already noticed Vanish Mode in the chat settings on Messenger, as Facebook has been rolling out it slowly to some users. And on Instagram, some elements of Vanish Mode are already part of the core direct messaging feature set, including disappearing photos and videos once a piece of media has been viewed.
The new feature will work both in group chats and personal conversations.