fast takeoff folks believe that we will only need a minimal seed AI that is capable of rewriting its source code, and recursively self-improving into superintelligence
Speaking only for myself, the minimal seed AI is a strawman of why I believe in “fast takeoff”. In the list of benchmarks you mentioned in your bet, I think APPS is one of the most important.
I think the “self-improving” part will come from the system “AI Researchers + code synthesis model” with a direct feedback loop (modulo enough hardware), cf. here. That’s the self-improving superintelligence.