So you want to use OpenRouter?

Choosing a model through OpenRouter does not necessarily choose a single implementation of its serving behavior. A developer's account describes provider differences in tool-call parsing and the conversation history accepted by the same model. An application can therefore encounter different integration failures when requests move between providers.

OpenRouter's routing documentation provides controls for this: provider.only restricts eligible providers, while require_parameters filters for support for the request's parameters. Those controls let developers narrow which backends they depend on, although a restricted pool also reduces the available fallback choices.