Yes, you will need to purchase it separately. Please check the Xbox Rewards FAQ for the full information:
How do I get the Xbox One version of Call of Duty®: GhostsGames on Demand?A. Buy the Xbox 360 digital version today from the Xbox Games Store and then upgrade to the Xbox One version of
Call of Duty®: Ghosts for just $9.99.
To redeem, buy the Xbox One version using the same Microsoft account on or before March 31, 2014. The discount will be automatically applied at check-out! The discount is non-transferable, not redeemable for cash, and cannot be combined with any other offer.
Limit one per Microsoft account.