You wanted to try three models from three vendors, so you did the sensible thing: pointed one client at a gateway, put one key in the environment, and stopped thinking about it. A gateway here is a service that speaks the OpenAI API and forwards your requests to Anthropic, Google, OpenAI, xAI and the rest, so switching models is a string change instead of a new SDK.
What almost nobody checks after that: what the gateway charges for the exact same tokens the vendor would have sold you directly.
What you actually buy from a gateway
Three things, and they are worth very different amounts.
One key and one invoice. Real, and boring. It saves you three signups and three billing pages.
