Facebook’s next updates for Messenger have a big focus on bots. Yep, Zuck is still trying to make “fetch” happen with those. Anyhow, the newest bits for the platform are mostly about letting others know that a bit of text originated from. That means from a shared bit of bot text will allow you to start a conversation with said bot from your existing conversation window. Even if you’re using Messenger from desktop. In addition to a bunch of other developer-centric notes is word that the bot text limit has been doubled. So yeah, jumping from 320 characters to 640 means that the bots are about to get a lot more chatty.
Source: Facebook Developers