Microsoft today claimed that there are now over 10 million people in the Windows Insider program. That’s a big jump from the previous numbers.

As you may recall from my article Next Up for the Windows Insider Program: Changing the World, Microsoft launched this program in October 2015 and the program had hit about 3 million people within a month. By the time of my interviews with Microsoft last November, I was told that there were about 7 million people in the Windows Insider program.

But now, just four months later, there are apparently over 10 million Windows Insiders.

“We count over 10 million Windows Insiders today, many of them fans, who test and use the latest build of Windows 10 on a daily basis,” Microsoft’s Yusuf Mehdi claims. “Their feedback comes fast and furious, they have a relentless bar of what they expect, but it so inspires our team and drives our very focus on a daily basis.”

I don’t actually believe that 3 million more people are suddenly testing Windows 10 builds now. Instead, I bet most of those new testers are actually on Xbox One: In November, Microsoft renamed its testing program to the Xbox Insiders program as part of a consolidation with the broader Windows Insiders program. A bit later, they opened it up so anyone could join. That, I think, accounts for the sudden rise in testers.

But no matter how or where the new testers are coming from, Windows Insiders is huge.

“To my knowledge, [the Windows Insider Program] is the largest public software preview program in the world, certainly the largest of its type,” Microsoft’s Gabe Aul told me in November. “It’s significantly bigger than anything Microsoft had ever done, and the number of downloads for Windows 10 preview releases is now hovering around the 100 million mark.”

Or as Dona Sarkar put it, “Insiders are the millions who represent the needs of the billions.”