Fringer released Firmware 2.21 today with support for the Contax 45-90mm f/4.5 and Contax 350mm f/4. The Fringer adapter now supports 35/3.5, 45/2.8, 55/3.5, 80/2, 120/4, 140/2.8, 210/4, 350/4, 45-90/4.5 and Mutar 1.4x. These lenses won’t be as fast as native lenses, but they get pretty close under the right conditions.
Release Notes:
2017/10/4
Version 2.21
1. 45-90/4.5 and 350/4 have been added to AF list. Now all the Contax 645 lenses can AF on GFX50s (Except the MF lens 120/4)
You can buy an adapter and download the firmware and directions from fringer.