A new build of Windows 10, number 10240, is now available to Windows Insiders on both the fast and slow track.

Microsoft has made no official statement—and may not even make any official statement—but the word from insiders speaking to Mary Jo Foley is that this build has been blessed as the release-to-manufacturing (RTM) build. That is to say, it's this build that will probably be found preinstalled on PCs on store shelves on Windows 10's July 29 launch day.

But the situation seems complicated, with Paul Thurrott tweeting that his sources say that the build hasn't yet been signed off—though with the broader distribution to Insiders, that may yet happen.

Hardware OEMs need a version of the operating system to preinstall, and that version has to be good enough even for a home user with no Internet connection. It can't be egregiously broken or unstable. But development of Windows 10 doesn't stop just because a version has been sent to the OEMs. There will almost certainly be a day one update for build 10240, but what there won't be, at least for a while, is another full Windows build that bumps the version number.