My experience matches your claim, but I've seen others recently claim cli use (shelled out from another harness though) showing clear extra-data billing.

And I'm fairly sure Anthropic did implement that though, at least for Claude SDK (which is/was a wrapper around claude -p); I was using the sdk for a product, and had a demo to show/ensure it was billed via subscription. I basically unset any API env vars, ensured the cli credential was in place, and spawned agents and watched the logs. When I re-ran it during that time period, it clearly went to extra data (there are messages in response logs calling it out).