Sigma recently released a new firmware update for Sigma MC-11 lens adapter. You can download this firmware here. This firmware update allows compatibility with the SIGMA 14mm F1.8 DG HSM | Art, SIGMA 24-70mm F2.8 DG OS HSM | Art, Cine Lens 14mm T2 FF EF mount and 135mm T2 FF EF mount from FF High Speed Prime Line.
That1cameraguy on Youtube has already posted the first two videos about the new Sigma MC-11 firmware tested on Sony Alpha a9 (Amazon/B&H Photo/Adorama) with Sigma lenses. The above video is a comparison between the previous firmware and the current firmware, and the below video is the new firmware at a sporting event.
The Sony a9 with updated Sigma Adapter is only firing at 10fps, not 20fps.