Motorola announced the Android 5.1 OTA a few weeks ago with a soak test in certain markets, but now US Cellular has posted update details on its site. Both the 2014 Moto X and Moto E LTE are getting the new build of Lollipop right now.

2015-05-26 15_46_00-Android Downloads _ Android-Powered Phones _ U.S. Cellular

You should be able to pull down the OTA by going into the system update menu. You can only get the update over WiFi and you need to be completely stock. Android 5.1 for these devices will make a few changes to the features, improve some UI quirks, and enhance stability. It's not a huge update, but it's nice to be completely up to date.