This is known as the release to manufacturing (RTM) stage. So what happens now? Well, it's a simple case of those device makers testing it out on their shiny new handsets and making sure everything's hunky-dory before getting it into the hands of us, the great phone-using public.
If you want proof Windows Phone 8 is in the bag, check out this image of team members autographing a sign -- a classic 'we did it guys' event.
There's no official word from Microsoft yet. When ZDNet contacted the Redmond-based company for comment, it replied it had "nothing to share at this time".
Microsoft is set to launch Windows Phone 8 on 29 October, with handsets expected to be available shortly after. It originally planned to launch in early October, along with Windows 8, but things slipped. So now -- fingers crossed -- everything looks to be on course.
Windows Phone 8 will face stiff competition from the iPhone 5, which goes on sale in less than a week, and iOS 6. And of course Android Jelly Bean, which will be a few months old by the time Windows Phone 8 launches.
Microsoft will vie with BlackBerry-maker RIM for third place on the mobile podium. RIM will launch BB10 early next year, so we could have quite a fight on our hands this winter.
Are you excited about Windows Phone 8? What would it have to do to tempt you from iOS or Android? Let me know in the comments or on our Facebook page.