Bring Your Own Key is a billing mode offered by AI gateways and routers such as OpenRouter: instead of the platform holding the provider relationship and charging a markup on top of usage, the customer plugs in their own OpenAI, Anthropic, or other provider API key. Requests still flow through the gateway's unified endpoint, routing logic, and analytics layer, but usage bills directly against the customer's own provider contract, negotiated rate, and data-processing terms — reducing or eliminating the platform's per-token markup in exchange for the customer managing more of the provider relationship themselves.