The Cult Mechanicus codex is not on the release schedule for pre-orders this week, so exactly how these new units we have been seeing will be fielded is still up in the air. It can only be assumed that the codex will come with next week's pre-orders, as we are getting some early insight to the Cult Mechanicus Detachments.
Please remember that these are rumors. This bit mentions the Canticles of the Omnissiah, which we had earlier rumors of. You can see what was said by following the link.
via anonymous sources on Faeit 212
the detachment for cult mechanicus gives you a reroll for warlord traits and to reuse a canticle of omnissiah once per game.
the detachment allows for a lot of the new kataphron units with up to 8 troop choices! thats going to be a crap load of shooting.
it looks something like this
compulsory 1 hq and 2 troops
optional 6 troops, 4 elites, 2 heavy support, and 1 fortification