Though Cortana isn't supposed to be officially available yet on the New Xbox One Experience (NXOE) for preview members, it appears that a pioneering Reddit user has discovered a trick to get the feature working. To enable Cortana, here are the directions given by Reddit user xbxo_zone:
For whatever reason, if you go to the settings tab on the guide, you can move up once. Hit the A button a few times and you will snap cortana.
If those instructions sound a bit vague, YouTuber Aussie Gamer has a nicely laid out instructional video, which we've embedded below:
It sounds strange, but we've tested it out and it does indeed work. As you can see in the screenshot up top and Instagram embed below, Cortana offers up all of the same neat tricks that she does on other platforms, even including the voice-activated "Hey Cortana."
If you want to try out Cortana, no matter how rough around the edges it is right now, we'd suggest checking this out as soon as possible. The feature isn't officially supposed to be included in the NXOE until early 2016, and there's no telling how long this will stick around before Microsoft does something about it.