X1 4k 120hz capable box?

Recently purchased a 4k TV with an available refresh rate of 120hz. From what I'm hearing outside of the xfinity community, the X1 4k dvr box (XG1v4-A) is only able to put out 4k resolution at 60hz or 2k resolution at 120hz. First, is this true? If true is there any planned rollout of a box capable of 4k at 120hz? Second, if false, does the hdmi cable that is sent out with the X1 4k box capable of 4k at 120hz, as it is not labeled or info available on the web.