From Sigma:
Sigma 18-35mm f/1.8 DC HSM Art Firmware v1.02
Autofocus is supported at any aperture value when used with the Canon Digital Cinema Camera EOS C100.
Note: Before upgrading the firmware of 18-35mm F1.8 DC HSM A013, please first update your SIGMA Optimization Pro to Ver1.2.0.
Download the Sigma 18-35mm f/1.8 DC HSM Art Firmware v1.02.
B&H carries the Sigma 18-35mm f/1.8 DC HSM Art lens.