API-Keys should only be used for models not included or when the usage limit was reached

Hey, I just figured something out, that to me is quite annoying. I want to use Opus 4 with an API key (because it is not available within the subscription), but I want to continue using my included subscription usage with Sonnet 4. But as soon as I add an API-Key, the API-Key is always used instead of the “Premium Message Usage”. I would really like to change that, so that I can use both Opus and Sonnet, without both using my API-key (only Opus should).
Thank you.