I'm not understanding your message. We don't call FORMAT_VALUE on constant strings in f"x is {x}" & FORMAT_VALUE doesn't take an argument. Are you saying in a hypothetical FORMAT_VALUE where BUILD_STRING takes a set of objects & applies formatting to them, thus allowing us to remove FORMAT_VALUE as an opcode? That seems like I'm imposing my own internal thoughts on what you're saying, but when I don't understand what someone's saying I'm prone to raise my own imaginations. Also note that f'{x}' compiles to 'LOAD X, FORMAT_VALUE' so there is no join lookup in the last benchmarks I posted

Nitpick about fstrtup2: it assumes compiler_joined_str's len is at least 2. Either an assert should be added or the last if-else should be `else if (len == 1)` instead of a plain `else`