From Sigma:
The Sigma Corporation would like to announce the development of the rear filter holder for the SIGMA 14mm F1.8 DG HSM | Art for Canon.
* Only available for the Canon mount lens. There are no plans for the development in SIGMA and Nikon mounts.
As more details of this rear filter holder become available, a further announcement will be made.
B&H has the Sigma 14mm f/1.8 DG HSM Art Lens available for preorder.