The original Moto X launched in 2013, and while the device is approaching the two year mark, it's still new enough for people to reasonably expect an upgrade to the newest Android releases.
Well, some owners on AT&T have taken to Google+ with screenshots of Android 5.1 coming to their hardware. The carrier has started soak testing the latest version of Lollipop in anticipation of a general rollout, but some recipients were able to get the goods without an invite.
As it turns out, the carrier has made the over-the-air update available to general users who attempt to pull it down manually.
The OTA will bump your phone up to software version 222.26.1. If you choose to wait, a notification should arrive automatically once AT&T has deemed the update ready for the general public. Either way, you can read the full release notes on Motorola's website.