While Twenty Twelve has been an anticipated feature of the upcoming WordPress 3.4 release, some will be disappointed to hear that the new default theme for this year will not ship with WordPress 3.4. Instead, it will likely come with WordPress 3.5. However, if you’re interested in playing around with the theme as is, you can download the source via GitHub. While no direct reasoning was given as to why the theme was punted, I’m going to guess that because 3.4 development is already behind, it made sense to postpone it to speed up the development of everything else going into 3.4.
Twenty Twelve To Be Released With WordPress 3.5