Dubbed Text Reply, this is a beta feature designed for iOS devices in mind. The idea is that with this feature, you can now reply text messages via your watch like the Pebble Time, Time Steel, or Time Round. You can choose to reply either via voice message, or a pre-defined text message that has already been setup.
However take note that there are several caveats. For starters this is a beta so expect some bugs. Secondly, it also seems to be applicable to those who are using AT&T as their phone line on their iPhones. This means that Verizon, Sprint, and T-Mobile users are out of luck. Thirdly, the messages will not appear in your iOS Messages app.
This is because of a partnership with AT&T, messages you send from your watch will be sent directly through AT&T, so if you’re the type that likes keeping a log of their messages, you’ll want to take note of this. In any case the update to the Pebble Time companion app and the firmware for your watch should already be available, so update them if you’d like to check this feature out.