Not long ago, Microsoft announced a change to the Windows Insider Program that would allow a select amount of Insiders to "skip ahead" to the next release of Windows 10 (codenamed Redstone 4) coming after the upcoming Fall Creators Update. Today, it appears the skip ahead program has reached capacity, as Microsoft is no longer accepting any new participants.
This means that Insiders who did not select skip ahead won't be able to do so now test out any Redstone 4 preview builds until after the Fall Creators Update is finalized, which we expect will happen sometime in September. Insiders who did jump into the skip ahead ring before it closed will continue to receive Redstone 4 builds from here on out, which over time will get progressively more buggy, as the Insider Program tends to do.
Once the Fall Creators Update is finalized, Microsoft will begin pushing Redstone 4 preview builds to all Insiders in the Fast ring, whether they selected skip ahead or not. But until then, these early Redstone 4 preview builds are now only available to a select, limited amount of Insiders. Now, the reason Microsoft is limiting capacity for the skip ahead option is so the company can continue to test the Fall Creators Update with Insiders and continue to receive feedback and telemetry on those last few builds.
If the skip ahead option was open to all, Microsoft may lose more Insiders to the Redstone 4 builds than needed at this time. Microsoft needs as many Insiders as possible to continue testing the last few Fall Creators Update builds for optimum quality assurance. So, did you choose to skip ahead to the next development cycle of Windows 10?