By technical editor Matt Allard:
There are still a lot of people using Final Cut Pro 7 several years after the release of FCPX. Apple has long since stopped supporting older legacy versions of Final Cut. Fortunately for users of FCP7, Apple have released an update to the Pro Video Formats available in Quicktime.
According to Alister Chapman over at XDCAM User FCP7 users now get native support for XAVC in FCP7 and Quicktime. This is great news if you still use FCP7 as you no longer need to transcode XAVC material into another format for editing.
On a Mac computer Using Quicktime Player 7 you can play back XAVC MXF files, even in 4K. You can only do this with Quicktime 7 as Quicktime Player 10 doesn’t recognise 4K XAVC clips at all and HD XAVC clips get transcoded to .mov first. You can download QT Player 7 here for XAVC playback.
According to Alister it currently looks like the support is mainly for XAVC-I.