The recently announced Fujifilm XF 8mm F3.5 R WR is the widest rectilinear prime lens for the X mount and the only other Fujifilm X mount lens that goes as wide is the XF 8-16mm F2.8 R LM WR but it comes with a huge size and weight disadvantage. Below is the scaled size comparison of these two and the Fujifilm XF 10-24mm F4 R OIS WR to better understand how these compare in real life, followed by a specs comparison:
As seen on the image, the new XF 8mm is significantly more compact and lighter than the other two, but lacks the focal flexibility of the zooms. I personally use my wideangle zoom lenses at the widest end most of the time so the more compact and affordable 8mm prime would be my choice if I had to choose between these three.
Fujifilm XF 8mm F3.5 WR vs XF 8-16mm F2.8 R LM WR vs XF 10-24mm F4 R WR Feature Comparison