The BMD 8K Pro can be configured in a few ways. You can configure it for 720p or 1080i(p) on all 4 outputs or you can run output one in 4k (Flex Ultra). You can not however run 4 independent outputs of 4K.
In a coming soon release, you will be able to run 8K using all four outputs (2x2 4K)
The BMD SDK does not allow the card to display four independent 4K videos at one time.