Shipping a Linux Kernel with Windows

Beginning with Windows Insiders builds this Summer, we will include an in-house custom-built Linux kernel to underpin the newest version of the Windows Subsystem for Linux (WSL). The kernel will be rebased at the designation of new long-term stable releases to ensure that the WSL kernel always has the latest Linux goodness. When the WSL kernel source becomes available it will consist of links to a set of patches in addition to the long-term stable source.

Source: devblogs.microsoft.com