The new build is JLS36I and so far, no other Nexus device has had either the update or the factory image. Don't expect anything exciting with Android 4.3.1 outside of a few bug kills and the usual stability enhancements. The fun begins with the Android 4.4 KitKat update which should be introduced along with the LG Nexus 5 later this month. One early rumor had October 14th as the date when both the phone and the latest Android OS build will be introduced.
source: GoogleDevelopers via AndroidCentral