AT&T has announced on its official blog, that it has started rolling out Windows Phone 8.1 update for the ATIV S Neo (SGH-i187). The update will bring much needed performance improvements and native features from Windows Phone 8.1 including Action Centre, Cortana, Internet Explorer 11, Word Flow keyboard, Start Screen personalisation options, extra column of Live Tiles, a file manager, and much more. There's no official changelog as of now, but if you are restless to get the update, you should try manually updating your device by going to Settings > Phone Update. Microsoft had released Windows Phone 8.1 update in the final form to developers in April 2014, and it reached general availability during July 2014.
The ATIV S Neo was released on November 8th in the US for AT&T, featuring Windows Phone 8, a 4.8-inch HD LCD display, 1.4GHz dual-core Qualcomm Snapdragon 400 processor, 1GB of RAM, 16GB of internal storage space, an 8-megapixel camera with 1080p video recording, a 1.2-megapixel front-facing camera, and a 2,000 mAh battery.