Honest question: is there a reason for the naming conventions for these models? Anything that makes it better than giving them names with model numbers, like “Claude 3” or such?

Yes.

Each of the nouns is a “size class” in literature. From small lines poem (haiku, sonnet) to larger story (fable) to very large story (opus) to culture-defining foundational (myth).

It’s a fun way to say how many parameters are in the model without revealing a number like 405B or 17B which isn’t really comparable vs other models.