GW has posted an introductory article on the Tau and their new units and technology.

"The Tau Empire has been growing rapidly over the last few centuries, and is now beginning to infringe on the domains of other major galactic powers, such as the Imperium of Man. The Tau seek to bring the wisdom of the Ethereals to the worlds of Mankind, but the Imperium will not listen. This new Codex takes us to the fringe of the galaxy, as the Tau gear up for their third period of expansion. They are mustering for war."