Today Games Workshop Digital Editions revealed part (half) of a page from the Sentinels of Terra codex supplement. What this reveals to us is that Sergeant Garadon is listed, and will be the first special character added by a codex supplement. There are also some special rules including Lysander's Specialist bolter drill that will be in it, and the ability to add additional Centurion Warsuits into your lists.
Check out the Image below.
This image is a released image by Games Workshop Digital Editions.