OpenRouter is a unified API service that provides developers with a single interface to access over 400 large language models (LLMs) from more than 60 providers, including OpenAI, Anthropic, Google, Meta, and Mistral. It simplifies the integration and optimization of AI models by offering features like cost management, automatic failover, and transparent, pay-as-you-go pricing. The platform aims to democratize access to AI models and streamline AI development workflows for businesses and individual developers.