This mini guide describes how to install the WordPress Twenty Fifteen theme from the Subversion repository within the shell.
Inside the terminal screen, go to your WordPress installation directory and run the following commands:
cd wp-content/themes/
svn co http://core.svn.wordpress.org/trunk/wp-content/themes/twentyfifteen/
remember you need to be on the nightly release 4.1-beta since the new theme uses functions that arent available to 4.0
or just download 4.1 beta 1 and it`s all included