Earlier this year, Microsoft posted/updated some information on the Hosted Pool (i.e. where you run your automated builds in Visual Studio Team Services – i.e. VSTS). One item of interest in that post is that the hosted XAML build controller is planned to be shut down sometime next month (September, 2016).
For accounts created after on or after April, 2016, access to the hosted XAML build controller was never provided, so this should not be an issue. However, if you have XAML builds running in VSTS, or were planning on migrating XAML builds to VSTS, you should take note.
Here is the excerpt I am referring to (emphasis is mine):
I’m looking for the hosted XAML build controller. Where did it go?
In September 2016 we plan to shut down the hosted XAML build controller. Accounts created on or after April 2016 do not have access to the hosted XAML build controller.
Note that you will still be able to make use of an on-premises build server to run XAML builds. You simply will not be able to run them in the hosted environment within VSTS.
Keep this in mind if you are considering migrating your existing XAML builds to VSTS and/or if you already have XAML builds running within VSTS.
You can read the full details here.