Variety reported the news with no specific details known.
Update: THR is reporting Cate Blanchett is in final negotiations with Marvel for Thor 3 to play a “bad-ass female.”
Blanchett recently starred in the Peter Jackson Hobbit and Lord of the Rings films.
Thor 3 has a November 3, 2017 release directed by Taika Waititi starring Chris Hemsworth, with Tom Hiddleston said to be back as Loki, and Mark Ruffalo as Banner and the Hulk.
Maybe Blanchett is up for Hela?