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.
Cohere API
API for Cohere's Command (generation) and Embed (embeddings) models. Strong focus on enterprise search, RAG, and classification use cases.