OpenAI

ChatGPT, the GPT-5.6 model family, multimodal models, and the Responses API.

OpenAI develops ChatGPT and a broad API platform spanning language, reasoning, coding, image, audio, and open-weight models. ChatGPT is the consumer product; developers build custom applications through the API, primarily with the Responses API for stateful and tool-using workflows.

GPT-5.6 family

GPT-5.6 is the main frontier model family for complex professional work. It uses three tiers with the same core generation:

GPT-5.6 Sol is the flagship option for the hardest reasoning, coding, and professional tasks. The gpt-5.6 API alias routes to Sol.
GPT-5.6 Terra balances capability, latency, and cost for production applications.
GPT-5.6 Luna targets efficient, high-volume workloads where lower cost is more important than maximum capability.

The family supports configurable reasoning, tool use, structured outputs, image input, and long-context workflows. The Responses API also supports multi-step agent patterns, including programmatic tool calling and a beta multi-agent mode.

Specialized models

OpenAI maintains separate model families for tasks that benefit from a dedicated interface:

GPT Image 2 generates and edits images.
GPT-Realtime 2.1 supports low-latency speech and tool-using conversations; related transcription and text-to-speech models cover focused audio tasks.
GPT-5.3-Codex is optimized for agentic software development.
gpt-oss-120b and gpt-oss-20b are open-weight reasoning models released under a permissive license.
Embedding and moderation models support semantic search, retrieval, clustering, and safety classification.

Platform shape

OpenAI combines a general assistant with developer infrastructure. Applications can stream responses, call functions, return schema-constrained data, search or retrieve files, and keep conversation state. This makes the platform suitable for both direct question answering and longer workflows in which a model uses tools and verifies intermediate results.

Model IDs and availability change independently between ChatGPT and the API. A ChatGPT model label should therefore not be treated as an API model name.