A new “Insider Fast Configuration update” is rolling out to Windows Insiders on Windows 10 Mobile Build 10549. You will receive this update if you are enrolled to “Insider Fast” or commonly known as Fast Ring in your Windows Insider app. So open your Windows Insider app and enroll to Insider Fast, if you are not receiving this update.
Coming to what this update brings in terms of changes, there is no changelog and no visible changes but last we heard from Gabe Aul that it makes Microsoft target your device in correct ring. . Hopefully it means Microsoft is planning to push some new build soon as mentioned by Gabe yesterday.