This is the XF 100-400mm f/4.5-5.6 OIS WR lens. For those unfamiliar with some of the terminology used by Fujifilm, this lens comes with optical image stabilization and given its max focal length of 400mm, which on a cropped sensor equates to 600mm, having built-in OIS will definitely come in handy to keep those photos from being blurry due to camera shake.
The “WR” also means that it is weather resistant, joining the likes of other Fujifilm XF lenses like the more recent 16mm f/1.4. Since zoom lenses are often used in sporting events and also in nature photography in the outdoors, having it weather resistant and paired with a camera like the Fujifilm X-T1 will be useful.
In terms of pricing, there has been no official confirmation but it will not come cheap. It is said to be priced at a whopping €1,800 and is expected to be announced on the 15th of January.