GPT‑5.6 brings Sol, Terra, and Luna to ChatGPT, Codex, and the API
OpenAI splits GPT‑5.6 into three tiers for maximum quality, balance, and efficiency-with new capabilities for agents and tool use.
OpenAI has made GPT‑5.6 generally available in ChatGPT, Codex, and the API. The family consists of Sol, Terra, and Luna: three tiers with different balances of capability, speed, and cost.
Three models, different roles
- Sol is the flagship for complex coding, research, design, and knowledge work.
- Terra balances intelligence and cost.
- Luna targets fast, high-volume processing.
In ChatGPT, Sol powers the higher reasoning settings, while Terra and Luna are also available in products including Codex and the API, depending on the plan.
More than a model update
GPT‑5.6 adds capabilities including programmatic tool calling, explicit prompt caching, persisted reasoning, and a multi-agent orchestration beta to the Responses API. These features make it easier to divide longer processes and coordinate multiple agents.
The practical lesson
The three-tier structure confirms a broader trend: one model for everything is giving way to a carefully composed stack. Good products use the largest model where it creates value and choose speed and predictable cost elsewhere.
Source: GPT‑5.6 at OpenAI.
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