To use GPT-6 Luna on the free plan, pick it in the ChatGPT desktop app. OpenAI gave it to the Free and Go plans, and the entry point is Work and Codex inside the desktop app — the model list in the regular chat window has no Luna option. Update the desktop app to the latest version first, then follow the three steps below.
Find Luna in three steps
First, open the ChatGPT desktop app on your computer and confirm you are signed in with a Free or Go account. Second, go to Work or Codex — do not stay in the regular chat window. Third, pick GPT-6 Luna from the model list, and you can start chatting right away. If it is not in the list, check whether the app is the latest version first, then confirm your plan; the gradual rollout may not have reached you yet.
What Luna, Terra, and Sol are each for
Luna is the lightweight model prepared for the Free and Go plans, good enough for everyday conversation, organizing material, and short writing. Terra is the fast, low-cost model launched on October 26, 2026, open only to Plus, Pro, Business, Enterprise, and Edu, used in Work and Codex — free-plan users cannot reach it. Sol is the everyday main model for paid plans, positioned above Luna. The three models are not replacements for one another; they are divided by plan: the free tier uses Luna, while paid tiers choose between Terra and Sol as needed.
Boundaries to know before you use it
Using Luna on the free plan costs nothing extra, but OpenAI has not published a message cap for the free plan — you will see a notice when you reach the limit. Calling Luna through the API is a different matter: the model name is gpt-6-luna, it is billed by usage at $0.10 per million input tokens and $0.50 per million output tokens, and no subscription covers that part. Not every entry point offers Luna; the desktop app is the most reliable one. If you cannot find it on the web or mobile app, check the desktop app first.
