Here's how to think about Redstone, based on what I'm hearing.
Windows 10, which was codenamed "Threshold," will be released this summer, Microsoft execs have said. My sources say there will be a minor update to Threshold some time this fall (which still will be known as "Threshold,"), in addition to the other, smaller regularly released fixes and updates that Microsoft will continue to provide before and after Windows 10 is released to manufacturing as part of its "Windows as a service" model.
Microsoft's current plan calls for a similar summer/fall release schedule for Windows next year. "Redstone" is the codename for those releases due in 2016. Redstone will not be "Windows 11" or "Windows 12." It will still likely be "Windows 10," I am hearing.
Redstone will be delivered automatically to Windows 10 users as part of their regular, every-month-or-so updates. Redstone will just be a larger update than the others and will provide new functionality and support for new classes of devices that aren't already part of Windows 10, so the supposed thinking goes.
Releasing regular updates to Windows 10 works well for things like Spartan (the new Windows 10 browser), messaging and the Start Menu -- things that increasingly are not part of the Windows core. But for deeper core work to support the devices building on top of Windows 10 -- things like Xbox Surface Hub, Windows Phone, and HoloLens -- sometimes bigger changes are needed that require bigger updates like Redstone.
Redstone also will be the vehicle for Windows core features that aren't going to make the cut in time to be included in Windows 10 this year.
My sources say the Windows Insiders program will continue throughout the Threshold/Redstone development/delivery/deployment timeframe, meaning Microsoft will continue to provide early test builds of not just the monthly updates, but the larger updates to Windows 10, too, into next year, and possibly beyond.
I asked Microsoft officials for comment on Redstone. No word back so far. Update: A spokesperson said the OS team had nothing to share re: Redstone.