Windows 10 Mobile Build 10166 is here and if you are in Insider Fast ring you will be able to install the update. But before you tap on “check for updates”, you need to go to Windows Insider app and reselect Insider Fast ring and then check for update. In case you are new to Windows 10 Mobile preview you need to follow our tutorial for updating to Windows 10 for Phones. Click here to read what Build 10166 brings in terms of changes over last preview build 10149.
The update takes around 30-35 minutes in getting downloaded over a good connection and may get stuck at times and then you may need to restart or do a soft reset and it may download again. The update is around 400-500 MB in size. So check whether you have up to 1 GB free on your device and your device should have battery charge of more than 40% for update to take place.
Installation and data migration takes another 40-55 minutes, so a bit of patience is needed. Post-upgrade migration status screen is back with Build 10166. It went quite smoothly for my Lumia 1020 but for Lumia 540 I needed to download and install the update twice.
Build 10166 screenshots gallery: