“Delete for everyone” effectively functions as an “unsend” button, although it will only work for seven minutes after hitting send the first time. The feature will be active both in single as well as group chats, for all kinds of messages (text, image, GIFs, etc.).
The message’s content will disappear from the conversation; however, WhatsApp will display a message that says “This message was deleted,” indicating that something was there (it’s unclear whether WhatsApp will show who the original sender was in a group chat).
There is also an additional caveat; the messages’ content will disappear from within the chats, but deleted messages will likely remain in notification previews. More careful users may still be able to look at a preview of the messages from their notification panel, but once opened only the “This message was deleted” label will greet them.
The feature will only work if both users (or all participants in a chat room) have the latest version of the app, on iOS, Android, and Windows Phone (Windows Mobile). There is no word on whether the feature will launch for WhatsApp web.