From the same Facebook user and group who confirmed that Zygarde is available in Australia and New Zealand, as well as Europe, the distribution of Zygarde 50% Forme also works in the US.
In light of this, we’re now encouraging everyone everywhere to see if Zygarde is working just like the last two Mythical Pokémon distributions did and that anyone anywhere can get their hands on the Pokémon. Should you succeed, Zygarde 50% Forme is perfectly compatible with both Pokémon X&Y and ORAS games. Still no end date has been confirmed so don’t leave it for too long, make sure you get out your 3DS and try now to see if you can get yours via the Nintendo Network! (Go “Mystery Gift” & “Get Via Internet”) Zygarde is a special gift who comes at Lv.100.
Even Serebii, one of the greatest Pokémon related news site is still waiting on details, so be sure to comment how you get on because we are all keen to hear whatever feedback there is.
Source: Two Assassins And A Potato Pokémon Kingdom (Facebook User)