This is what I've been wondering about for a while now. I have the 20x plan as well, which I thought would allow me to try some API coding - but you get zero API usage.

As you said, I would imagine where the token usage comes from is irrelevant - you are generating the same load whether you do it from claude code or some other agent. So it seems like the rules are more to do with encouraging claude code usage, rather then claude model usage.