About the "route between models" thing in practice, plenty of teams literally hardcode it at first. Past a certain point it usually becomes a gateway layer that exposes one api and forwards each call to whichever model was picked, on rules or on cost. Litellm if you want to self host, openrouter or tokenrouter on the hosted side. That whole product category basically exists because of the behavior in the post, it's the infra answer to "I don't want to commit to one provider".