Today, Microsoft pushed an update to its Windows Phone 8.1 Preview, and advises all those who already installed the new OS to “to stay current on the latest build” - which, by the way, is now build number 12397. This is the third update that WP 8.1 Preview is getting since the beginning of May. The previous ones brought small enhancements, including improved battery life. The new update doesn’t offer visible changes, as it merely tweaks some APIs, while also “enabling some newly commercialized devices.”
Most Windows Phone 8 users should start receiving the final, non-Preview version of WP 8.1 in the coming weeks or months. The OS brings lots of novelties, like the Cortana personal assistant, a new notifications center called Action Center, customizable lock screen, Internet Explorer 11, and so on.
source: Windows Phone Blog via Phone Scoop