As the names suggests, one can deduce that one of the devices will be bigger than the other.
This means that the 5-inch foldable display can fold out to 7-inches and transform into a small tablet.
There are also rumors that it will have biometric sensors for fingers, face, iris and palm.
However, there is no news yet on how big would the Galaxy X1+ be.
source: www.techworm.net