https://techcrunch.com/2018/11/14/how-facebook-messenger-remove-works/

Facebook secretly retracted messages sent by CEO Mark Zuckerberg, TechCrunch reported seven months ago. Now for the first time, Facebook Messenger users will get the power to unsend too so they can remove their sent messages from the recipient’s inbox. Messages can only be unsent for the first ten minutes after they’re delivered so that you can correct a mistake or remove something you accidentally pushed, but you won’t be able to edit ancient history. Using the Formally known as “Remove For Everyone”, the button also leaves a ‘tombstone’ indicating a message was retracted. And to prevent bullies from using the feature to cover their tracks, Facebook will retain unsent messages for a short period of time so if they’re reported, it can review them for policy violations.

The Remove feature rolls out in Poland, Bolivia, Colombia, and Lithuania today on Messenger for iOS and Android. A Facebook spokesperson tells me the plan is to roll it out globally as soon as possible, though that may be influenced by the holiday App Store update cut off. In the meantime, it’s also working on more unsend features, potentially including the ability to preemptively set an expiration date for specific messages or entire threads.