Newest Xperia X Concept update adds Ambient mode, features multiple fixes1
That aside, the update comes with a bunch of fixes. After installing it, the camera viewfinder will have a fixed brightness level independant of your current brightness setting. A Bluetooth audio issue present when using "Ok Google" voice commands is eradicated, and there are fixes for tinted display colors and LED notifications for missing calls.
The update brings the software version to 38.3.A.0.94 and weighs in at about 40MB. Oddly enough, it contains the January Android security patches, despite Sony having already issued this month's security updates. But such is the unpredictable nature of Concept software.