This is a feature release. It changes the licensing model for Xamarin as announced during the Build 2016 keynote to enable Xamarin features for all Visual Studio users (including Visual Studio Community Edition users) at no extra cost! See the blog post (https://blog.xamarin.com/xamarin-for-all/) and the FAQ (https://www.xamarin.com/faq) for additional details.
For Visual Studio, the new Xamarin licensing model is compatible with any non-Express version of Visual Studio 2013 or 2015. For Xamarin Studio, it requires the latest version of Xamarin Studio as listed under "Release Info" below.
"System.FormatException: One of the identified items was in an invalid format. at Xamarin.Components.Ide.Activation.ActivationService.GetErrorWorkflow". This problem happens when attempting to use the new licensing model with old incompatible versions of Xamarin. Solution: Ensure that you have updated all of your installed Xamarin packages on both Windows and Mac to match the versions listed under "Release Info" below.
"Requires a Business (or higher) license". (One common scenario where this happens is if you already have Xamarin installed and then update to Visual Studio 2015 Update 2. In that case the Visual Studio update process will not automatically update the Xamarin extensions. This behavior will be adjusted in the future.) Solution: Ensure that you have updated all of your installed Xamarin packages on both Windows and Mac to match the versions listed under "Release Info" below.
"bash: ... Broker/126.96.36.199/Broker.exe: Permission denied" or "bash: Broker/188.8.131.52/Broker.exe: cannot execute binary file" when attempting to connect to the Mac build host from Visual Studio. Solution: Make sure you have installed all of the required Xcode and Xamarin packages on the Mac build host: https://developer.xamarin.com/guides/ios/getting_started/installation/mac/.
"System.ArgumentNullException: Value cannot be null. Parameter name: path1 ... at Xamarin.Messaging.Activation.ActivationAgent.InitializeMonotouchActivation ()" Solution: Make sure you have installed all of the required Xcode and Xamarin packages on the Mac build host: https://developer.xamarin.com/guides/ios/getting_started/installation/mac/.
"The remote server returned an error: (403) Forbidden" or "Access Denied" when installing Xamarin. Status: FIXED. The Xamarin team has updated the stale server-side information that was causing this problem. The changes should now be fully propagated to all the CDN servers. If anyone is still seeing this error, please add a comment below to let us know!
The remaining known issues are the same as for "Cycle 6 – Service Release 2". Please see that thread for details.
If you find any new issues in this release compared to the previous Stable versions that you would like the Xamarin team to investigate, please do file a quick bug report, and then feel free to add a note on this thread with the bug number. Thanks!
As usual, existing Xamarin Business, Xamarin Indie, or Xamarin Enterprise users can downgrade back to the previous Stable versions if needed by manually reinstalling each old package. See the KB article on downgrading.
New users will all want to stay on Cycle 6 – Service Release 3 or later to continue using the new licensing model.
Release Blog post: https://releases.xamarin.com/stable-release-cycle-6-service-release-3
(The reamining compatibility notes are the same as for the "iOS 9.3 and Xcode 9.3 SDK Bindings" release.)
[iOS] Xcode 7.3 requires OS X 10.11 El Capitan.
[XamarinVS] The Cycle 6 builds of XamarinVS now require Visual Studio 2012 or higher. Following along with the end of Mainstream Support for Visual Studio 2010 by Microsoft, Cycle 6 is not compatible with VS 2010.
[iOS] The Cycle 6 builds now require Xcode 7 or higher. For example, attempting to build an iOS app for device using Xcode 6.4 will now fail with "Native linking failed, undefined symbol: ___divdc3".
[Xamarin Studio] [XamarinVS] [iOS] [Android] [Xamarin.Mac] Support for OS X 10.9 Mavericks has been deprecated. The Cycle 6 builds now require OS X 10.10 Yosemite.
EDIT Mar 31: Add information about "The remote server returned an error: (403) Forbidden" and "Access Denied".
EDIT Mar 31: Update status of "The remote server returned an error: (403) Forbidden" as FIXED.
EDIT Apr 01: Update compatibility notes and common issues.