OpenRouter’s core feature is automatic routing of requests to different model backend providers. This routing is designed to optimize for cost and leverage the specific optimizations of each provider. Mohamed Moustafa has identified potential issues arising from differences in serving software and configurations across providers. These differences can lead to variations in model behavior, particularly concerning vision capabilities and reasoning effort processing. The provider.only option provides a mechanism to control which provider is selected for a given model ID. The /endpoints method returns the list of available providers for a specific model ID.
Source: https://simonwillison.net/2026/Sep/11/so-you-want-to-use-openrouter/