The new 2x teleconverter and the 1.4x are only compatible with XF 50-140mm and the 100-400mm. Paired to the 50-140mm, the 2x teleconverter will produce a field-of-view equivalent to that of a 100-240mm lens (or a full-frame equivalent of 150-360mm) at f/5.6 aperture, while producing a 200-800mm f/9-11 FOV when paired with the 100-400mm.
Fuji film states that the 2x teleconverter is constructed of nine elements in five groups, and is able to double the effective reach while maintaining the optical performance of the original lens. Impressive stuff for a camera company known for outstanding image quality.
Phase-detect autofocus capability is maintained with the 50-140mm and the 2x teleconverter, while the AF is listed to contrast detect with the 100-400mm.