The Sony Xperia Z1s is a model similar to the Sony Xperia Z1, with some minor cosmetic changes. The phone also is IP58 certified for protection against dust and water, allowing it to survive a submersion to as deep as 5 feet of water for as long as 30 minutes.
When the phone launched, it came out of the box with Android 4.3 installed, so the update to Android 4.4.4 is the model's first foray into the world of KitKat. You will need to sync your handset to a computer to receive the update, so head over to www.sonymobile.com/update to get the ball rolling.
source: XperiaBlog via AndroidCentral