This depends on how you define both atheism and agnosticism
(Gnosis is the ancient Greek word for “knowledge“ and agnosis the ancient Greek word for the lack of knowledge/the opposite of knowledge)
Another definition of agnostic atheism is one who does not believe in a God, but cannot know for sure there is no God, because such a thing is unknowable (as one cannot disprove a negative), whereas gnostic atheism is one who does not believe in a God, and believes they do know there is no God for lack of any evidence, or due to some other evidence which they believe proves such a thing impossible.
This depends on how you define both atheism and agnosticism
(Gnosis is the ancient Greek word for “knowledge“ and agnosis the ancient Greek word for the lack of knowledge/the opposite of knowledge)
Another definition of agnostic atheism is one who does not believe in a God, but cannot know for sure there is no God, because such a thing is unknowable (as one cannot disprove a negative), whereas gnostic atheism is one who does not believe in a God, and believes they do know there is no God for lack of any evidence, or due to some other evidence which they believe proves such a thing impossible.
This goes into more detail:
https://en.wikipedia.org/wiki/Agnostic_atheism
As with any belief system (or lack thereof) it can become a tangled mess of epistemology and philosophy and even attempts at tautology.