Magic Lantern made April fools of us all by going live with an experimental build for the Canon EOS 5D Mark III on April 1st. It's in early stages of development but it's the real deal, and brings experimental Raw 4K video recording to the 5D III, among other things.

The build adds the following recording resolutions to the camera:

1920x960 @ 50p (both 1:1 crop and full-frame - 3x3 pixel binning)
1920x800 @ 60p (same as above)
1920x1080 @ 45p and 48p (3x3 binning)
1920x1920 @ 24p (1:1 square crop)
3072x1920 @ 24p (1:1 crop)
3840x1600 @ 24p (1:1 crop)
4096x2560 @ 12.5p (1:1 crop)
4096x1440 @ 25p (1:1 crop)

Once downloaded, it'll look like this:

Stills shooters will also find a 'full-resolution LiveView' mode that shoots 5796x3870 at 7.4 fps. Magic Lantern notes that this mode is usable at fast shutter speeds, but comes with rolling shutter.

Magic Lantern states that anyone who downloads the build should know that it's still quite bleeding edge, with plenty of bugs to work through. And of course, ML also wants you to know that using their software will probably void your warranty.