Microsoft explains this change writing, "We are now at the point of the development cycle for the Windows 10 Fall Creators Update where our focus is now on stabilization for release to the world." What that means for Insiders is that builds will be released more quickly, but they will feature mostly bug fixes. Only participants who join the Skip Ahead program will get the RS_PRERLEASE builds moving forward.
Microsoft notes that the development for RS4 has only just begun, so builds for that RS_PRERELEASE branch won't be on the same pace as builds for RS3_RELEASE branch. If Skip Ahead sounds like something you want to be in, you are too late. Microsoft wrote, "Skip Ahead is now full so if you try to join, it will let you know that in the Settings app. But don’t worry! Once the Windows 10 Fall Creators Update is released, Skip Ahead goes away and all Insiders in the Fast ring will get moved back to the RS_PRERELEASE branch for RS4."
Build 16273 brings with it some new items that Microsoft wants testers to focus on, including emoji notification by adding the Windows Insider Emoji Bot to your taskbar in My People. The release brings with it a new font called Bahnschrift, which allows you to have an entire typeface family in a single file bringing infinite variability. This means you can have an infinite range of font styles rather than being limited to Light, Regular, and Bold weights.
A slew of Windows Shell improvements have been made with this release with too many bug fixes to mention individually and a similar number of fixes have been applied to Microsoft Edge along with input improvements. One of the biggest new feature additions in this release is that View Mixed Reality is now part of Windows 10. The preview build of the feature is available for users in Skip Ahead and allows users to bring 3D content into the real world with the View Mixed Reality capability.
Microsoft wrote, "Anyone flighting View 3D with View Mixed Reality enabled will now have the ability to take any creation from Paint 3D and see it come to life. Quick loops between the apps allow you to refine and tweak your model helping you capture the ultimate moment."
Windows 10 S is also part of the Insider Program now with users being able to install preview builds of Windows 10 S just as you can for Windows 10. "Windows Insiders can try Windows 10 S on their PCs and join the Windows Insider Program via Settings > Update & security > Windows Insider Program to receive Insider Preview builds for Windows 10 S just as they would on other editions of Windows 10."