The current speculation is that the Sony Xperia Z1s is actually a refreshed version of the Xperia Z1 with certain ports moved and the phone's dimensions increased. Right now, the only different sized version of the Sony Xperia Z1 that has been introduced is the mini-sized Sony Xperia Z1 f for Japan's Docomo. The difference between this model and the full-sized Xperia Z1 is the smaller 4.3 inch screen, the lower 720 x 1280 resolution, and the smaller capacity 2300mAh battery.
Loaded with a Qualcomm Snapdragon 800 CPU and 2GB of RAM, the Sony D5503 scored a very impressive 34,193 on the AnTuTu benchmark site, showing that even a "mini" phone can be a powerhouse. Meanwhile, the Xperia Z1s refreshed model scored a higher 35,485 on AnTuTu. And another version of the phone, possibly for U.S. markets, scored a whopping 36,257. This model is allegedly the Sony Xperia Z1 LTE (C6916) supposedly heading for T-Mobile.
Thanks, Anonymous Tipster!
source: Digi-Wo (translated), XperiaGuide,