Please see https://releases.xamarin.com/stable-release-cycle-8-service-release-0/ for the details about this release, including the steps to update or downgrade as needed.
Please file a quick bug report using the "Cycle 8" new bug form if you see any behavior that looks suspicious in these versions (and if it isn't clear whether one of the known issues in the release notes matches the problem).
Comment in this forum thread if your question is not related to a suspicious behavior after installation, but instead one of the following:
[Xamarin for Visual Studio], [Xamarin Studio] - 43566 - The iOS Designer initialization process will cause any running iOS 10 simulator to become non-responsive. The designer initialization happens when opening an iOS project in Xamarin Studio and during the connection to the remote Mac in Visual Studio. This issue does not affect Xcode 7.3, iOS 9.3 (and lower) simulators.
Improved in this release: Cycle 8 Service Release 0 includes some fixes to reduce the chances of hitting this problem, but additional fixes are also planned.
Workaround: Quit and restart the simulator after the designer has initialized. You can then proceed to use the simulator again as normal.
You can view all of the remaining bugs that have been reported against the Cycle 8 version that are not yet fixed in "Cycle 8 – Service Release 0" using the following Bugzilla query:
Note that some of the remaining issues on this list are already marked "FIXED." The candidate fixes for those issues are not yet included in this release, but they will be included in a future Service Release or Feature Release.
[Xamarin for Visual Studio] - 44300 - Xamarin.Android projects appear as "Incompatible" after closing and reopening a solution in a single VS session. Visual Studio's ActivityLog.xml file shows "LegacySitePackage failed for package [XamarinAndroidPackage] ... Method not found: ... Mono.AndroidTools.AnalyticsService.ReportContextProperty(System.String, System.String) ...".
Updated Oct 04: A candidate fix for this issue has now been published to the Stable channel in version 18.104.22.1683. A potential remaining issue involving Test Recorder remains under investigation, so it is recommended to uninstall Test Recorder if you continue to see this issue after the update.
Old partial workaround: Deleting the contents of %LOCALAPPDATA%\Microsoft\VisualStudio\14.0\ComponentModelCache and then closing and opening Visual Studio again will allow the Android project to load. Note that closing and re-opening the solution again in this new session can cause the issue to re-occur.
[Xamarin Studio] - 44285 - Xcode 8 quits after Xamarin Studio returns to the foreground when using Xcode 8 via Open With > Xcode Interface Builder.
[Xamarin.Android] - 44633 - "Deployment failed because of an internal error: Failure [INSTALL_FAILED_DEXOPT]" when
<AndroidUseSharedRuntime> is enabled in certain projects because classes.dex is not deployed to device as expected.
[Mono], [Xamarin.iOS], [Xamarin.Android], [Xamarin.Mac] - 44708 - "TrustFailure (The authentication or decryption has failed.) ... Invalid certificate received from server." with "Error code: 0x5" or "Error code: 0xffffffff800b010f" when attempting to access HTTPS servers on ports other than 443
[Xamarin for Visual Studio] - 44535 - "'System.ComponentModel.INotifyPropertyChanged' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.ObjectModel" for projects that reference PCLs with