By Microsoft's own accounting, it is adding more than 100 million Windows 10 devices to the fold per year en route to that elusive (so far) goal of hitting 1 billion devices. The number now stands at 800 million, and while that is still 200 million short of where Microsoft had hoped to reach in relatively short fashion, Windows 10 is the fastest growing version of Windows ever.
That's not really a surprise, given how aggressively Microsoft pushed to get Windows 10 on as many devices as possible from the very beginning. For the first year, Microsoft even gave Windows 10 away as a free upgrade to Windows 7 and Windows 8/8.1 users, and extended the courtesy even longer for users with accessibility needs.
Barring a change in strategy, Windows 10 is and will continue to be the last monolithic version of Windows. Instead of releasing brand new releases every few years, Microsoft has committed to rolling out major updates with new features twice a year, the next of which will be the 19H1 update. And of course there are the monthly Patch Tuesday security updates.
In the early going, Microsoft ambitiously figured it would hit 1 billion Windows 10 devices within the first 2-3 years of its release. That time frame has already come and gone, and even free upgrades could not push adoption as fast as Microsoft initially anticipated. However, Windows 10 was able to leapfrog Windows 7 last year, to become the most widely used version of Windows on the planet.
Hitting 1 billion devices does seem inevitable at this point, though. In June of last year, Microsoft boasted it had extended Windows 10's reach to more than 700 million devices, and just seven months before that it was talking about having reached 600 million devices. If Microsoft is able to maintain that pace, Windows 10 could conceivably extend to 1 billion devices in late 2020 or early 2021.
Bear in mind that these numbers include all devices that are runny any variant of Windows 10, which include desktops, laptops, convertibles, 2-in-1s, Xbox One consoles, HoloLens headsets, and so forth. It is still quite the achievement, though, and speaks to Microsoft's strategy of unifying hardware around a single ecosystem.