As announced on Apple’s developer news site, Apple has just released Xcode 8.3 final.
Xamarin is proceeding as usual to test for compatibility and publish an updated version of Xamarin.iOS for any modified or new APIs in Xcode. Keep an eye on this blog for status updates.
UPDATE March 28: Corresponding new versions of Xamarin.iOS, Xamarin for Visual Studio, and Xamarin Studio are now available. See the release announcement for additional details.