Two weeks ago, Microsoft announced more big changes to the Windows Insider Program. It's ditching the Fast, Slow, and Release Preview rings and replacing them with the Dev, Beta, and Release Preview channels. Today, those changes are going live.
Hey Folks - Channels have arrived! Expect the changes to land in your #WindowsInsider settings over the next few hours. Remember, we've done the mapping for you, so there's no direct change you need to make. Check out blog for details! ^AL https://t.co/auc8wvrxRy— Windows Insider (@windowsinsider) June 29, 2020
The way that the program works isn't changing though. It's really just changing the names of things to make them more accurate to what the Insider Program has become. With the Fast and Slow rings, the names implied a particular cadence to how often you'd get new builds, and that hasn't been the case for a while.
The Dev channel is for prerelease builds. These are the big builds that Microsoft pushes out every week with new features. They're not tied to a feature update (they are tied to a development branch, but that's neither here nor there) until they get to a build number that gets promoted to the Beta channel. Once it's in the Beta channel, it will be serviced until it should be ready for release, and then it will be promoted to the Release Preview channel for final testing before general availability.
Again, that's how the Windows Insider Program has already been working for a while now, only with the Fast and Slow rings instead of Dev and Beta. The new channels are simply meant to be more accurate, thanks to the way that the program has changed over the years.