GPT-6 Astra vs Sol vs Luna: Which OpenAI Model to Use
Astra at $10/$50, Sol (now 6.1) at $2/$10 and Luna at $0.10/$0.50 per million tokens. What separates them and which plans include each.
OpenAI's GPT-6 family arrived in three steps: GPT-6 Astra on September 3, 2026, GPT-6 Sol and GPT-6 Luna on September 22, and GPT-6.1 Sol on September 29. They are tiers of one family, not rivals, so the choice comes down to how hard the task is and how much you run it.
The three tiers
| Model | What OpenAI built it for | API input / output per 1M tokens |
|---|---|---|
| GPT-6 Astra | Its most intelligent model, for the most demanding professional work | $10 / $50 |
| GPT-6.1 Sol | Near-Astra results on coding, computer use and professional work | $2 / $10 |
| GPT-6 Luna | Fast, efficient everyday work at scale | $0.10 / $0.50 |
Who gets which in ChatGPT
- Astra: Plus, Pro, Business and Enterprise, inside each plan's existing allowance, with extra usage on credits. Pro, Business and Enterprise also get Astra Pro.
- Sol: Plus, Pro, Business, Enterprise and Edu, in ChatGPT Work and Codex.
- Luna: the same paid plans, and Free and Go users in the ChatGPT desktop app.
How to choose
- Luna for high-volume, simple jobs: classifying, summarising, extracting fields, short replies. At $0.10 per million input tokens it is the cheapest model in the family by a wide margin.
- Sol for almost everything else, including agents that edit code and use a computer. OpenAI prices it at a fifth of Astra.
- Astra for the long, ambiguous jobs where one wrong call is expensive: a large migration, a financial model, a legal document. OpenAI also lists it as its first model to reach the Critical cybersecurity capability threshold under its Preparedness Framework, so expect stricter safeguards on security work.
Running them in your own tools
The Codex API packs ($5.99 for 50M tokens over two days) suit a burst of agent work in Codex CLI or Cursor through a gateway. For a full year of models inside an editor, see Cursor Pro+.
Frequently asked questions
Is Luna just an older model?
No. OpenAI built Sol and Luna to bring Astra's advances to cheaper, faster models.
Does Astra cost extra on ChatGPT Plus?
Astra usage counts against the plan's allowance; OpenAI sells credits for usage beyond it.
Related guides
- GPT-6.1 Sol Explained: Who Gets It, What It Costs, How to Use It
- Cheapest Way to Use Frontier AI in October 2026: API Prices Compared
- GPT-6.1 Sol vs Claude Opus 5.5 vs Gemini 4 Argon: Frontier Models Compared
- Monthly and Short-Term AI Plans: Try a Tool Before a Year
- Personal AI Agents Compared: Muse vs Grok Bot vs Hermes vs OpenClaw vs Manus
- ChatGPT Plus and SuperGrok Ready Accounts: What to Do After Login