One account for every model: one key, one Base URL, four protocols

What an aggregator really sells is not model access but a single contract: one key, one balance, one bill, four protocols. That is what makes a multi-model stack affordable to operate.

• Collapse it to three things: key management, base_url override, protocol choice.
• Protocols are only four families; every vendor maps into one of them.
• When not to aggregate: hard latency SLAs, data residency, or vendor-only features.