Microsoft is currently beta-testing Redstone 2 in Insider builds, which are now almost feature-complete. These builds began rolling out in September, and the latest feature update includes many new enhancements. As Microsoft prepares to release this update, several pre-release processes need to be completed. According to a report from MSpoweruser, the Creators Update is scheduled to be released on April 11, indicating that it is feature complete and nearing the final sign-off. The report also suggests that the final sign-off will occur sometime next week.
April 11 is the same date as when Windows Vista retires, and Windows 10 Creators update releases. It is worth noting that Microsoft has also started working on Redstone 3, the details of which can be read here.
