Panasonic GX9 has a 20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine processor. On the other hand, Panasonic GX85 has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine processor.
Another similarity between these two cameras is that both Panasonic GX85 and Panasonic GX9 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the GX9 and GX85 sensor size comparison.
Panasonic GX9 and Panasonic GX85 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Panasonic GX85 has 27% larger pixel area (14.21µm2 vs 11.16µm2) compared to Panasonic GX9, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.