We just reported about Windows 10 Mobile Build 10166 changes from the Emulator build and now Microsoft has made it available for Windows Insiders in Fast Ring. Here is the official changelog.
Build 10166 official changelog:
There are lots of small changes and feature tweaks in this build, but our major focus over the past few builds on mobile has been about improvements to core quality.
Most of the known issues we listed for Build 10149 have been fixed. We also fixed the issue where the post-upgrade migration status screen was missing, which made the Lock screen appear frozen without the date and time for up to 10 minutes. The post-upgrade migration status screen should appear normally now. We also fixed the issue where you were unable to unlock your phone after entering your PIN and it keeps letting you type even though you entered your pin correctly that was caused by a TPM issue. The colors in apps should now appear correctly including in including the titlebar in the Outlook Mail app which is no longer orange. And we also improved reliability of app downloads and updates from the Store (which is now no longer marked as “Beta” and the old Store has been removed).
We also got a lot of feedback about the size of the battery icon, so we bumped that up a bit larger to make it easier for everyone to see.