So it's been confirmed for ages now, and filming has already gone and done.
Its due for release in the summer this year.
There will be 3 episodes.
Cassie from season 1 and 2 will have an episode.
Cook from season 3 and 4 also has on.
Effy from 1 to 4 has an episode to.
I for one am glad mainly for Cooks episode because i hope it will somehow say or even show what atleast happen to him and Dr John Foster.
When season 4 ended nobody knew if Cook himself died but clearly because of the new episode for him means he didnt die.
more infomation here http://skins.wikia.com/wiki/Series_7