I say new in a very loose way - these are pretty much verbatim from the current print versions that are out there. There is one small and very important difference though - there are no rules for allies in either codex. WHAT?
You heard right, there are no rules that allow Space Marines or Imperial Guard to take units out of either codex. The Witch Hunters codex still has rules for allowing you to induct a certain few units from the Imperial Guard of Space Marine Codex, but not the other way around.
I am excited that Games Workshop put these books up for download. Hopefully this is some kind of experiment and maybe we will see more of this in the future. I don't hold much faith for this, but you gotta have hope.