The Lumix GX-8 replaces the well-received GX-7, and the upgrades are noteworthy. They've crammed a few more megapixels into the camera: 20.3, up from 16.
Other upgrades include a slightly higher frames-per-second burst mode, an electronic shutter that can capture at speeds of up to 1/16,000th of a second, and a lower base ISO (100 vs 125 on the GX7). You can find a good comparison chart here if you want all the spec changes.

The biggest upgrades? 4k video, and dual stabilisation!