On Anunnaki Wikipedia page we can read:
Their relation to the group of gods known as the Igigi is unclear – at times the names are used synonymously but in the Atra-Hasis flood myth the Igigi are the sixth generation of the gods who have to work for the Anunnaki, rebelling after 40 days and replaced by the creation of humans.
Jeremy Black and Anthony Green offer a slightly different perspective on the Igigi and the Anunnaki, writing that "lgigu or Igigi is a term introduced in the Old Babylonian Period as a name for the (ten) "great gods".
In the Epic of Creation, it is said that there are 300 lgigu of heaven.
In this answer we can read that scientists believe that there could be as many as 750 Anunnaki.
Therefore, what is the difference between Igigi and Anunnaki, can anybody elaborate that?
Were they different group of deities or Igigi were just the lower class of Anunnaki?