From what I've seen the pricing is intentionally hostile towards third party, and therefore provider-agnostic, code agents. I have never used "Claude Code" or "Google Antimatter" or whatever it's called, I only use OpenCode, but I think the intent behind them and the reason only they, and not API access, is included in their static pricing is very transparent. If you want API access you are forced to pay-as-you-go, and many "normal people" do not want that. My way of solving it is simply using OpenRouter, setting up blacklists for models and pretty strict spending limits.