ok so is fable 5 the same as sonnet 5 or not, the names are frying my brain

genuine question because i cant get a straight answer. sonnet 5 became the default june 30. fable 5 got pulled june 12 and came back july 1. are these two names for one model or two totally different models? and when people say "the nerf" are they talking about fable 5 specifically or the whole thing? i keep seeing all four words claude opus sonnet fable thrown around like everyone already agreed what they mean.