On May 2, 2019, Niantic announced that Azelf, Mesprit, and Uxie will be arriving in raids in a regional capacity. From now until May 27, 2019:

Uxie will be available in Asia-Pacific region

Mesprit will be available in Europe, Middle East, and Africa

Azelf will be available in the Americas and Greenland

They will also continue to be available in the wild.