Earlier this year at CES,Lenovo took the wraps off their latest lineup of premium commerce course notebooks, and they revamped the X1 lineup completely. Originally the X1 was just the X1 Carbon notebook, and but Lenovo has decided to expand the X1 series to include the X1 Carbon,the X1 Yoga and X1 Tablet. So the ThinkPad Yoga is now the ThinkPad X1 Yoga, and as such it keeps the same thin and light design of the X1 Carbon.
Source: anandtech.com