Apparently a bigger update than the ones before … took me some time to get in installed (and it restarted at a time that I didn’t expect, I got on my feet to get me some coffee and when I returned the restart screen was welcoming me back forcing me to wait at least 15 minutes before I was able to continue my work).
Anyway … it is a Preview Build released to Fast Ring and the Skip Ahead subscribers. These builds will be from the rs_prerelease for RS4 (Redstone 4) and it was announced that from now on Fast Ring and Skip Ahead will get builds at the same time. My guess is that over time the Fast Ring will merge into Skip Ahead and Skip Ahead will go away (to maybe return before moving over to RS5 – if they will continue using the naming Redstone paradigm)
This build is also the first one with somewhat more visible changes, especially in the Settings area. No need to copy all the changes here, they are all collected in the official release post: