No, a "derived work" is a legal concept, it means "you copied the original". Being inspired by, or even deliberately designing for API compatibility with an ori

No, a "derived work" is a legal concept, it means "you copied the original". Being inspired by, or even deliberately designing for API compatibility with an original work is not "derivation" nor is it "copying", as far as copyright law is concerned. Remember only certain portions of the original are eligible for copyright in the first place, e.g. APIs are not, module or class structure is not, ideas are not. It's important to remember that copyright law protects works from being copied, not from being read. Clean room is a legal tactic used against an aggressive adversary, it's not something that's at all necessary or appropriate in the general case.