The new version of iMovie features:
The 10.1 update is available in the Mac App Store and is free to users of iMovie 9 or later. iMovie for Mac is $15.
Macworld will have a review of the new version of iMovie for Mac coming soon.
Roman Loyola
Apple releases iMovie update with 4K video support, new user interface
13.10.2015
On the heels of the release of the new 21.5-inch Retina 4K iMac and the new Magic input devices, Apple has updated iMovie for Mac to version 10.1.