The new raid in patch 10.1 is called Aberrus, the Shadowed Crucible and consists of 9 bosses. This raid has four difficulties: Raid Finder, Normal, Heroic and Mythic.
The raid comes out when Season 2 starts, which is one week after the patch 10.1 goes live:
May 9, in US servers
May 10, in EU servers
All four raid difficulties will start at the same time. Raid Finder will be divided in wings with some bosses in each wing. These wings will not be released the same time.
Raid Finder Wing 1 is called "The Discarded Works" and comes out:
May 9, in US servers
May 10, in EU servers
Wing 1 consists of following bosses:
Kazzara, the Hellforged The Amalgamation Chamber The Forgotten Experiments)
Raid Finder Wing 2 is called "Fury of Giants" and comes out:
May 23, in US servers
May 24, in EU servers
Wing 2 consists of following bosses:
Assault of the Zaqali Rashok the Elder The Vigilant Steward, Zskarn
Raid Finder Wing 3 is called "Neltharion’s Shadow" and comes out:
June 6, in US servers
June 7, in EU servers
Wing 3 consists of following bosses:
Magmorax Echo of Neltharion
Raid Finder Wing 4 is called "Edge of the Void" and comes out: