https://www.cnet.com/news/panasonic-lumix-gh5s-hits-new-lows-at-ces-2018-and-thats-good/

While the size-to-capability balance of Micro Four Thirds cameras really can't be beat, the smaller-than-APS-C-size sensors can be a drag in low light. 

With Sony's full-frame, low-light-champion A7S II as competition, Panasonic took a necessary step backward. It created a 10.2-megapixel Four Thirds sensor for the Lumix GH5S, about half the resolution of the 20MP version in the GH5 in order to increase the low-light sensitivity to a native ISO 51,200 -- only a stop short of the larger sensor in the Sony. It also allows the camera to support 14-bit raw stills, something that's been lacking in Micro Four Thirds models as well, which have been stuck at 12-bit for a while.