GOOGLE WILL DEVELOP THE ANDROID OS FULLY IN PRIVATE, AND HERE'S WHY

Summary from the TLDR newsletter

Google is doing away with its current two-pronged Android development strategy and instead shifting all development internally starting next week. The company previously maintained a public branch and an internal development branch, which resulted in Google spending a lot of time and effort merging patches between the two branches. This change doesn't mean that Google is becoming closed-source - the company will continue to publish the source code for new Android releases, but the frequency of public source code releases for specific Android components will change.