Below you can see the front-view size comparison of the Fujifilm GFX 100 and Pentax K-1 II. The Pentax K-1 II is clearly the smaller of the two cameras. Its body is 19 mm narrower, 54 mm shorter and 17 mm thinner than the Fujifilm GFX 100.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.