Tracking the Xbox's sales has been much trickier than with its two generational competitors, largely down to Microsoft's decision in 2015 to stop reporting sales figures for the console. Up to that point, they'd only published figures for the One's first year, between November 2013 and November 2014. In that time, the One had sold 10 million units, compared to the almost 15 million shifted by Sony in that same time.
Now, an industry analyst, per WccfTech, has said that NPD data that is unavailable to the public pegs the Xbox One at around 35 million sales. This would suggest that not only has the PS4 comprehensively outsold the Xbox, but that its initial market share (selling around 50% more consoles in its first year) has increased. The PS4 appears to have outsold the Xbox 2:1.
The Xbox One came up against some teething issues when launching, including packaging the original console with the expensive Kinect sensor which has since been discontinued. Since then, the new versions, the One S and One X, have been met with a positive reception. However, the Xbox has come in for criticism for its lack of major exclusive titles. Though decidedly second-best compared to the PS4, looking at the all-time best selling console list offers a rosier picture. The One has comfortably outsold the original Xbox and the much-loved N64. It also has the SNES in its sights, particularly if it's likely to stick around for the next few years.
Another bright spot is the Xbox One X, which is reportedly outselling the PS4 Pro in the US. This doesn't quite square with what we saw over Black Friday, although those numbers were skewed heavily by the various discounts and deals available.