A Spotify representative declined to comment on the leaks, and Microsoft offered the following (very teasy) statement: "We're always working on a number of new experiences for Xbox One owners, many times with great music playing in the background, but have nothing to announce today".
A certain eagle eyed Reddit user posted an image that shows Major Nelson - otherwise known as Xbox Live Director of Programming Larry Hyrb - using the app on Xbox One. That could mean that Spotify's full release is just around the corner. Spotify for Xbox One is indeed coming soon and being tested internally at the moment.
It seems that a Spotify Xbox One App is finally inbound. It likely has something to do with Microsoft's efforts with Groove Music.
Though we have no idea what to expect from an Xbox One version of the Spotify app, we have some ideas based on how it works on the PlayStation 4.
It seems likely Microsoft realized that shutting Spotify out of the platform isn't going to significantly contribute to Groove's growth, and meanwhile not having Spotify is a possible competitive disadvantage when potential customers are deciding between an Xbox and PlayStation purchase.