This is not an announcement of a new product, Sigma is just letting us know that the Arca compatible foot for the Sigma 150-600 f/5-6.3 OS Sport is now available and retailers should have it soon.
From Sigma:
We are pleased to announce the availability of TRIPOD SOCKET TS-81 that is the optional lens foot which can be attached to the SIGMA 150-600mm F5-6.3 DG OS HSM | Sports. It is compatible with the Arca Swiss quick release plate and the clamp. The deliberately designed length of its rail provides the flexibility to adjust the center of gravity making it balance perfectly, even while zooming or using accessories, such as a tele converter and battery pack. Consideration has been given to the portability and transportation of the lens when Tripod Socket TS-81 is attached. The lens hood can still be reversed and the lens stored in its original padded case, even with the Tripod Socket TS-81 attached. Incorporated into the Tripod Socket are safety stopper screws to prevent the lens from falling. There are 2 sizes of screw holes, 1/4 and 3/8, making it compatible with tripods other than Arca Swiss, too. When it is compared to the supplied tripod socket, it offers more space between the lens and device, and the change of grip has improved the usage as a handle for carrying.
Source: [The-Digital-Picture]