The Anunnaki were a group of deities in ancient Mesopotamian culture.
How many of them were there at the peak time (which we know about)?
For example on Wikipedia page we can read:
In the Epic of Creation, it is said that there are 300 lgigu of heaven.
Based on excavation and digs we have currently found over 560 deities. However scientist believe that there could be as many as 750.
According to Bottéro's book titled: Religion in Ancient Mesopotamia
A Sumerian list of around 560 deities that did this was uncovered at Fâra and Tell Abû Ṣalābīkh and dated to circa 2600 BCE, ranking five primary deities as being of particular importance.
