Maker of the GPT family and the most widely adopted commercial LLM API.
Category: Foundation Models · Type: Foundation model provider · Website: https://openai.com
Overview
OpenAI builds the GPT series of large language and multimodal models and exposes them through a developer API and the ChatGPT product. Its models are the default reasoning engine for a large share of agents in production, and its function-calling and Responses APIs set many of the conventions other providers follow. The flagship as of mid-2026 is GPT-5.5.
Key Features
- Frontier GPT text, vision, audio, and reasoning models
- Function/tool calling and structured outputs that agents depend on
- Responses API and the built-in Agents SDK for agent orchestration
- Realtime, embeddings, and image/audio models in one platform
Role in the Agentic AI Stack
A primary 'brain' that agent frameworks, coding agents, and enterprise platforms call. OpenAI also ships its own orchestration via the Agents SDK and coding agent OpenAI Codex.
Part of Agentic AI Landscape → Foundation Models