Quoting wowhead:
so to get the 25man version of the tier sets, you have to a) be able to get the token and b) purchase the 10man version of the set.Tier 10 sets will come, like Tier 8, in two varieties: a Normal and Heroic set -- or T10 and T10.5.
T10 is going to be purchasable with Emblems of Frost (much like the lowest T9 set), and those Emblems will drop off both 10- and 25-player versions of Icecrown Citadel, as well as from the first random Heroic dungeon you do each day.
T10.5 will be purchasable with tokens, several classes grouped in the same token - like in Ulduar - and the tokens will only drop in the 25-player version of Icecrown Citadel, of course. The only difference will be the requirement that you will have to upgrade a T10 item you already have, to a T10.5 one. So you will need to first spend the Emblems, and then hope to get a token needed for the upgrade.
I like this change.. i've bought 10man tier gear, only to have the 25man tier equivilant drop the next day for me, now there is no need to worry, since you need the 10man gear anyway!