Anthropic only authorizes their own Claude code to be used with a subsidized subscription.
They want you to use and get accustomed to only their own tools. If other coding harnesses were allowed, it's far too easy to switch providers.
They can't allow that, because they only have a few months of head start.
So everyone accepts Claude code which is required for these sweet subsidized tokens.
That is old. Every harness (herdr, paseo, pi, etc) uses claude through the Agent SDK, and this draws from your subscription, not API pricing. If you're thinking of going with the "but Anthropic could ban every user doing this", if it's good enough for Google to slap it in Android Studio for everyone to use, it's good enough for you in literally any other harness.