Stage 1 - MVPs & Select Customers This is the second phase and will include MVPs and select top customers who have opted in. Program managers are again responsible for emailing the users.
Stage 2 - Private Preview Private preview is used for major new features and services and is designed to test new features with a broader set of customers that we don't have regular contact with. There are many ways to collect a list of customers for a private preview - from forum interaction, blog comments, etc. We've also done invitation codes, publicized email aliases for customers to request access, as we did for SSH access, and sometimes create in-product "opt-in" experiences for customers, as we’ve done for the new navigation UI. Individual teams will manage and communicate directly with their private preview customers.
Stage 3 - Public Preview Public preview is a state reserved for major new features and services where we want to gather feedback but are not yet ready to provide a full SLA, etc. Public Preview features are enabled for all VSTS customers but their main entry points in the UI are annotated with a "preview" designation so that customers understand this is not a completed feature. When a feature enters public preview, it is announced in the VSTS news feed and may also be accompanied by marketing communication, depending on the feature.
Stage 4 - General Availability (GA) GA denotes when a feature/service is available to all customers and fully supported (SLA, etc).