Despite earlier reports that Unity would be coming to Xbox One "later this year", it seems support for the feature will not be rolled out until some undisclosed point in 2014.
In a statement to Gamasutra Unity CEO David Helgason commented:
"During an interview with OXM in July, I misspoke and suggested that Unity for Xbox One would be available sometime in 2013. At that time, work had only just begun on those tools so while there will be a very few developers in very early testing phases this year, the Xbox One tools for Unity will not be widely available to developers until 2014.
"We are currently hard at work on the technology and are making great progress but we are not yet ready to announce any specific release windows. I apologize for any confusion my statement may have caused."
Developers who allow Microsoft Game Studios to publish their titles will receive free Unity dev kits for both Xbox 360 and Xbox One. Unity support is currently also free for both Windows Phone and Windows Store.