Like other Facebook app components, such as automatically generated captions for video ads, the M reply buttons are created using artificial intelligence — Facebook isn't actually running a contact center full of people who are following your Messenger conversations and thinking up possible answers for you on the fly. (At a high level, the system checks to see if a quick reply will be valuable in response to an incoming message, then figures out which possible replies would work, and finally makes its final suggestions based on your personal writing style.)
Facebook isn't first to come up with this concept. Alphabet's Google started adding it to widely used apps first. While this is the first time "quick replies" are coming to a Facebook service, Google's "smart reply" feature has appeared in the Allo messaging app, Inbox by Gmail, Android Wear, and the Gmail mobile app.
Microsoft-owned LinkedIn has also brought automatically generated replies into its messaging feature. Some companies have experimented with the idea in the world of enterprise software, specifically in the domain of customer service.
The difference with Facebook's move is that Messenger is massively popular, with 1.3 billion monthly active users. If Google's expanding use of the technology for messaging and email is any indicator, then the feature will also pick up adoption in Messenger, and it could end up in Instagram and WhatsApp as well.
In addition to quick replies, Messenger's M assistant will also start suggesting animated GIFs to share in conversations, and when you're talking about movies, M will also begin suggesting you open the Fandango chat extension to watch trailers, check showtimes and buy tickets.
For now, these new features — which build on enhancements in June — are only rolling out to people in the U.S.