Pedantically, agnostic atheism means that you don’t assert you know there isn’t a god (“I don’t believe there’s a god”) vs gnostic atheism having a positive assertion there definitely isn’t one (“There is no god”, usually followed by some logical argument).

Antitheism is the position that theism should be opposed, not what you described and it’s a philosophical position (which could be argued is a type of belief but that’s straying from the topic).