Call of Duty has posted a new blog entry that covers not only some of the highlights of the latest patch notes, but also digs into some detail regarding how DLC and Season Pass content works this year. This information was already announced last year, but now that we're at the point of purchase for a lot of people, it's important to restate, and I'm glad they did. Quoting directly:
If you are a Call of Duty: Ghosts DLC Season Pass holder, then your Onslaught DLC Pack will carry over from Xbox 360 to Xbox One. However, if you are not a Call of Duty Ghosts DLC Season Pass holder and purchase the Onslaught DLC Pack individually, it will not carry over from Xbox 360 to Xbox One. Currently, Microsoft only supports DLC transfer between Xbox 360 and Xbox One if you are a Season Pass holder. The Call of Duty: Ghosts Onslaught DLC Pack will carry over from PlayStation®3 to PlayStation®4 whether you purchase it individually or get it as part of the Call of Duty: Ghosts DLC Season Pass.
So, just to be super clear, because I do not want people regretting their choices:
Season Pass on Xbox One WILL NOT carry back to Xbox 360. The offer is only valid for people moving from the previous system to the latest system.
Season Pass on PS4 MIGHT? carry back to PS3. UPDATE: I am being told by fans that Sony offering one Season Pass on both PS3 and PS4. I have no reason to doubt them, but I was not expecting this offer. Nice deal -- we'll find out for sure when the content actually goes live.
Individually purchased DLC packs WILL NOT transfer between systems. If you buy Onslaught on Xbox 360 "a la carte," you do not also own it on Xbox One, or vice versa. (Again, we'll see what happens at the Sony DLC release to see if their rules are different.)
Season Pass WILL NOT upgrade across/between platforms by different manufacturers (i.e. Xbox 360 to PS4).
I want your Ghosts DLC experience to be happy and regret-free, so that's why I added bold type and festive colors. Now that you have the knowledge, please spread it around and prevent your friends from making expensive mistakes!