According to various online rumours Canon will release a new version of the current Canon EF 400mm f/5.6L USM in 2016. The new version will have Image Stabilization (IS) and will be lighter than the current non-IS version.
Current Canon EF 400mm f/5.6L USM Lens Image
Photos with the Canon EF 400mm f/5.6L USM Lens - View>>