According to those in the know, the first two handsets that will support XLTE will be the Samsung Galaxy S5 and the HTC One (M8). While an OTA update is supposedly required, that is a detail that has yet to be confirmed by the tipsters behind the story.
The XLTE network is expected to offer twice the bandwidth in certain U.S. cities. In addition, peak speeds will be faster on XLTE than on Verizon's current LTE pipeline. Customers won't have to change any settings to access the new network, which will eventually work on most of the new smartphones released by Verizon over the last year. And don't look for a new XLTE icon on your phone. For now, at least, those using an XLTE pipeline will show the current 4G LTE icon on their status bar.
Verizon is rumored to be introducing its next-gen LTE network, called XLTE, on May 19th
source: DroidLife via AndroidandMe