They announced the following 10 new cards in the lifestream:
Roche: Mercyless (5)
Destroy a face-down Ambush unit, then draw a card.
Updated Version:
Roche: Mercyless (6)
Destroy a face-down Ambush unit.
Yennefer: Necromancer (5)
Ressurect a Bronze or Silver Soldier from your opponent's graveyard.
Imlerith: Sabbath (5)
Duell the Highest enemy on turn end. If this unit survives, Heal it by 2 and give it 2 Armor.
2 Armor.
Triss: Telekinesis (6)
Create a Bronze special card from either player's starting deck.
Dandelion: Poet (6)
Draw a card, then play a card.
Cerys: Fearless (6)
Ressurect the next card you Discard.
Morenn: Forest Child (6,gold)
Ambush: When the opponent plays a Bronze or Silver special card, flip over and cancel its ability.
Geralt: Professional (7)
Deal 4 damage to an enemy. If it's a Monster unit, destroy it instead.
Ihuarraquax (7)
Deal 5 damage self.
When this unit's current power equals its base power, deal 7 damage to 3 random units.
Dandellion: Vainglory (9)
Boost self by 3 for every Geralt, Yennefer, Triss and Zoltan in your starting deck.
Also, if I didn't get it wrong, these will be all the new cards, which is a little bit disappointing, as the Midwinter update is already over 2 month in the past a bit more new cards would do the game good in my opinion.
Also, I'm not that happy that there will be even more cards that are designed specifically for Arena, as they still will be available in kegs and this will reduce the chance of getting usefull golds.
Edit: Thanks for the missing information, I added them.