At its annual shareholder meeting, Microsoft CEO Satya Nadella revealed that Windows 10 is installed and actively used on over 600 million devices worldwide. We say "devices", because Microsoft is counting PCs, tablets, smartphones and even Xbox One consoles that run the Windows 10 codebase in that tally.
Windows 10 installs started off strong, and 75 million devices were running the operating system within one month of launch. Within six months, the number had swollen to 200 million, and by the one-year mark, Microsoft was sitting at 350 million installs.
However, Microsoft never quite achieved the adoption rate that it originally forecast. The company originally stated that there would be over a billion devices running Windows 10 by the summer of 2018. But given that Windows 10 installs hit 500 million the past May following the launch of the Creators Update, and that we are just now cresting 600 million, it's unlikely that we'll see one billion installs by next summer – or ever at this point.
Microsoft lays most of the blame for this shortfall at the feet of its failed smartphone revival with Windows 10 Mobile and its now defunct Lumia smartphones. “We're pleased with our progress to date, but due to the focusing of our phone hardware business, it will take longer than FY18 for us to reach our goal of 1 billion monthly active devices,” said Microsoft’s Yusuf Mehdi back in July 2016.