Microsoft has just released the latest RS5 build, 17713, and with it comes a significant change for some Windows Insiders. Since the release of the Windows 10 April 2018 Update, the Insider Fast and Skip Ahead rings have been on parallel tracks, but as of today, just like with earlier versions (RS3 and RS4), Fast Ring and Skip Ahead will diverge.
If you're currently on the Fast Ring, you'll continue to receive Insider builds, although they have been renamed slightly, to "RS5_Release."
For Insiders on the Skip Ahead Ring, things are a bit different than previous iterations. This time, Microsoft is doing a complete reset of the Skip Ahead program:
Insiders who previously opted in to Skip Ahead will be automatically put back into the Fast ring. The option to join Skip Ahead will disappear from the dropdown under Settings > Update & Security > Windows Insider Program. In the coming weeks, we will make an announcement that we have re-opened Skip Ahead for Insiders to opt-in. If you were previously in Skip Ahead, you will need to opt-in again.
What the reset does is clear the decks and the Skip Ahead program will start fresh "in the coming weeks," with all Insiders having to opt-in to the program all over again. This will allow some Insiders who were left out of the Skip Ahead program to gain access, but it may and probably will leave some previous Skip Ahead testers out in the cold. We'll keep you informed on when the new Skip Ahead opt-in option becomes available, but if you want to get the latest bits, you're going to have to be on your toes.