From Sigma:
Thank you for purchasing and using our products.
We would like to announce the update in the lens firmware of the 150-600mm f/5-6.3 DG OS HSM | Sports CANON and 150-600mm f/5-6.3 DG OS HSM | Contemporary CANON on the SIGMA Optimization Pro, the dedicated software for the SIGMA USB DOCK.
The latest firmware update enables the lens to improve the AF accuracy when attached to the TELE CONVERTER TC-1401.
For those customers who own the following products, please update the firmware of the lens via the SIGMA Optimization Pro.
Applicable products
Benefit of this firmware update
It has improved the AF accuracy when attached to the TELE CONVERTER TC-1401.
You can download the latest version of the software from the following page:
SIGMA Optimization Pro Download page
B&H carries the Sigma USB Dock.