Azure OpenAI
Azure OpenAI Service provides access to GPT-4o, o1, and other OpenAI models hosted within Microsoft Azure, offering enterprise-grade SLAs, data privacy guarantees, and compliance certifications. It's the default choice for enterprises on Azure that need OpenAI models.
OpenAI API
API access to GPT-5, GPT-5.5, o3/o4 reasoning models, and the Responses API; plus embeddings, image, audio, and Realtime endpoints. The most widely deployed LLM API in production.