From Sigma:
Thank you for purchasing and using our products. We would like to announce a firmware update for the SIGMA MOUNT CONVERTER MC-11 EF-E.
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.
For customers who own the SIGMA MOUNT CONVERTER MC-11 EF-E, please update the firmware via SIGMA Optimization Pro by connecting it to a computer using the supplied USB Cable.
* Before updating the MC-11 firmware, please ensure SIGMA Optimization Pro has been updated to ver. 1.4.1 or later for Windows, and ver. 1.4.0 or later for Macintosh from the following download page.
SIGMA Optimization Pro Download page
Benefits of this firmware update
B&H carries the Sigma MC-11 EF-E Mount Converter.