As a reminder, we are initially making new mobile builds from our Development Branch available only to devices that shipped with Windows 10 Mobile. Currently this includes the Lumia 950, 950 XL, 650, 550, and Xiaomi Mi4. Today we are also adding support for the ALCATEL ONETOUCH Fierce XL. We plan to expand to other devices once we start releasing Windows 10 Mobile to other devices. If you are a Windows Insider on a device not mentioned above, you can stay in the Fast ring and sit tight until we expand to other devices or go back to Build 10586 and switch to the Release Preview Ring to continue helping us test Cumulative Updates. For more information about our rings and branches, I highly recommend reading
this post here in Insider Hub.