From Guifi.net - English Wiki
Actually it is only available the 32 bits version, however you can create the 64 bits version by following these steps:
First, download the generation system (or image builder):
apt-get install build-essential live-build imagemagick curl debootstrap git unzip git clone http://dev.cloudy.community/guifi.net/cloudy-image-builder.git
Now you have to do a little modification to the Makefile file:
ARCH ?= amd64 FLAVOUR ?= amd64
Finally, you can build the image with this command:
Once the image has been created, you have a 64 bits version of Cloudy in ./devel/binary.hybrid.iso
Otherwise you can "Cloudynize" a 64 bits Debian or Debian based system to turn it into Cloudy.
Read how to in the Cloudynize wiki page.