Windows Insider Program

Windows Insider Program is an initiative by Microsoft that allows users of Windows 10, Windows 11, and Windows Server to opt into testing out new, unfinished versions of the operating system. The first build to be publicly released via the Insider Program was Windows 10 build 9841.

Channels
The Insider program allows users to pick the builds they want to receive by enrolling to a specific channel. The Insider infrastructure is also used for Microsoft's internal selfhosting effort, with internal channels receiving builds both before and after the public channels; however, they are not a formal part of the Insider program.
 * Dev (formerly Fast Ring): This is the first channel in the Insider program to receive builds from the current development cycle. Between 2017 and 2019 an option called Skip Ahead also existed, which allowed a limited number of users to receive builds from the next development cycle, while the rest received builds from the stabilization stage of the current cycle.
 * Beta (formerly Slow Ring): This channel receives builds of the next Windows 11 feature update. If both Dev and Beta channels track the same development cycle, the Beta channel usually gets the same builds after being tested in the Dev channel.
 * Release Preview: This channel receives new app and OS updates (including feature updates) prior to their general rollout to consumers. It is the newest Insider channel, being introduced in 2016. Following the release of Windows 11, it is the only channel to receive new pre-release Windows 10 updates.