Microsoft is announcing today that 500 million active machines are now running Windows 10. The latest statistic comes almost 8 months after the company revealed 400 million devices were running Windows 10. Microsoft revealed its latest Windows 10 figures just as the software maker starts its Build developer event in Seattle today.

Microsoft had originally claimed it would have 1 billion devices running Windows 10 by 2018. The bold estimate was revised last July, with Microsoft admitting "it will take longer than FY18 for us to reach our goal of 1 billion monthly active devices." It now seems this will take a lot longer than 2018 for Microsoft to reach 1 billion Windows 10 devices. Growth has stalled since the free Windows 10 upgrade offer, and Microsoft has all but given up on phones that could have helped boost its numbers.

Sources familiar with Microsoft’s plans tell The Verge that the company has been loosely targeting 550 million monthly active Windows 10 devices by the end of June, and 575 million by the end of September. Today’s 500 million figure shows the company is roughly on schedule with its revised estimates, and it’s a large number of devices that makes it increasingly harder for developers to ignore.

Microsoft will now again try and tempt developers to create Universal Windows Apps for its Windows 10 operating system, while also convincing them to port existing desktop apps into the Windows Store. Build is a key event for this type of push, and the majority of Microsoft’s Windows focus will be seen tomorrow during the company’s second keynote at 11AM ET / 8AM PT.