Now that the Windows 10 Anniversary Update has been released to the public, Microsoft is getting to work on two more feature updates for the OS, both of which will launch in 2017.
The two updates are reportedly codenamed 'Redstone 2' and 'Redstone 3', continuing Microsoft's use of their "Redstone" naming scheme that began with the update now known as the Anniversary Update. According to information from Windows Central, Redstone 2 will launch in early 2017, while Microsoft is targeting a summer 2017 launch for Redstone 3.
Considering there might only be 4-6 months between Redstone 2 and 3, the latter release will most likely be a smaller update than Redstone 2.
Current reports suggest Microsoft is already in the process of developing Redstone 2, and will release the first preview build of the updated OS to Insiders shortly. The first builds of Redstone 2 probably won't have too many new or interesting features, but it will set the ball rolling and get valuable feedback in the hands of Microsoft.
The release schedule for Windows 10 in 2017 fits right in with Microsoft's plans to deliver Windows as a service to its users. Rather than bundling a ton of new features into a brand new operating system every couple of years, Microsoft wants to deliver new functionality to users as soon as possible. More frequent updates, such as biannual Redstone releases, is one way to do this.