GPT-6* (*which one?)

ChatGPT’s model menu says GPT-6. Depending on your plan and where you use it, that can mean Sol or Luna, in an October or a September version.

Two matching jars with blank clay labels marked by asterisks, one showing a sun, the other a moon
One name on the menu. Four versions behind it.

Your model menu says GPT-6. Ask which one.

What happened

On October 7, OpenAI posted on X: “GPT-6 and Intelligent UI, now rolling out in ChatGPT for everyone.”

The rollout is staged. OpenAI’s announcement says GPT-6 “starts rolling out globally to ChatGPT Plus, Pro, Business and Enterprise tiers today in the Chat tab. Starting tomorrow, the rollout expands to Free and Go tiers.” That puts Free and Go on October 8, with no timing per account. OpenAI’s help center says that if GPT-6 is not in the model menu, “it may not be available for your account yet.”

Behind the single name are two models. From OpenAI’s announcement: “GPT-6 in ChatGPT is powered by GPT-6 Sol for Plus, Pro, Business, and Enterprise tiers, and GPT-6 Luna for Free and Go tiers.” Go is a paid plan, and it still gets Luna. The menu won’t tell you which. The help center: “Look for GPT-6 in the model menu; it is not labeled Sol.”

OpenAI says both models are “tuned for everyday conversation.” Engadget goes further and describes Luna as not as capable as Sol.

There is a second layer. GPT-6 Sol and GPT-6 Luna first reached ChatGPT Work and Codex on September 22, according to OpenAI’s release notes. Its Deployment Safety Hub says the new models “will replace GPT-5.6 Sol and GPT-5.6 Luna in ChatGPT,” and that users “accessing GPT-6 Sol and GPT-6 Luna in Codex, and via ChatGPT Work, are still using previously released versions.” The system card tells them apart by month: “October for the versions released today, and September for the versions that remain in use in Codex and Work.”

Older choices also stay put. Per the help center, existing Latest selections move to GPT-6, “explicit GPT-5.6 Sol selections stay on GPT-5.6,” and “older selectable models are not being retired by this rollout.”

The asterisks

1. One name, four versions. In Chat on Plus, Pro, Business or Enterprise, GPT-6 means GPT-6 Sol, October version. In Chat on Free or Go, once the rollout arrives, it means GPT-6 Luna, October version. In Codex or ChatGPT Work, GPT-6 Sol and GPT-6 Luna are the September versions. OpenAI documents all four. The month never appears in the name.

2. A verdict without a plan is unverifiable. Posts calling GPT-6 brilliant or disappointing rarely say which plan or surface was used. A test on a Free account, a client’s Plus account, and a Codex agent can all be “GPT-6” and still be different models. Without those two details, the verdict cannot be checked or compared.

3. Pins and upper tiers add more names. A paid user who explicitly selected GPT-5.6 Sol stays on it. On Pro, Business and Enterprise, the Pro thinking option uses GPT-6 Pro, which OpenAI’s help center says is powered by GPT-6 Astra. Work and Codex also offer GPT-6.1 Sol, which OpenAI says “is separate from” the Chat options.

4. Staged means uneven. Until the rollout reaches an account, a Free or Go user may still be on the previous default. A test on October 8 may not match the same account a week later. Even OpenAI’s help page, as of October 8, still says Free and Go users receive GPT-5.6 Luna.

What this means if you ship

For a solo operator, the model name is a spec, not a brand. Build a workflow on a Free account and hand it to a client on Plus, and you tested on Luna while the client runs Sol. Run GPT-6 Sol or Luna in Codex, and you get a September version, not the October model you have been chatting with. OpenAI’s system card labels the October and September versions separately. So should you.

The same goes for what you read. A benchmark, a thread or a client complaint about “GPT-6” is a data point with a missing field. Ask for the field before you act on it.

What to do Monday

  1. Confirm your plan and surface. Check your plan and the model name shown, and note whether you are in Chat, Work or Codex.
  2. Name the model when you share a result. Write “GPT-6 Sol, Chat” or “GPT-6 Luna, Codex (September version),” not “GPT-6.” Ask for the same when you read one.
  3. Test on the client’s plan. If the client is on Plus and you are on Free, your results come from a different model.
  4. Replace GPT-5.5 before October 14. OpenAI’s models page says GPT-5.5 retires from ChatGPT, ChatGPT Work and Codex on all plans that day. The OpenAI API is not affected. For Codex with ChatGPT sign-in, the page points Plus and higher plans to GPT-6 Sol (gpt-6-sol) and Free and Go to GPT-6 Luna (gpt-6-luna). Check saved model settings, workspace defaults, custom agents, scheduled tasks and scripts.
  5. Decide about pins on purpose. An explicit GPT-5.6 Sol selection stays on GPT-5.6. Keep it if you need consistency, and switch if you want GPT-6.

GPT-6 is a family name. Ask for the first name.

Sources

Next: Usage* (*the agent re-reads your whole chat, every turn)