Claude Mythos, Fable and Opus 5.5: every Claude model, explained
Three releases in six weeks, plus the model most people can't use. Prices and plans included.
Which GPT-6 model you get in ChatGPT, and what Intelligent UI does
OpenAI's sixth-generation models reached the main ChatGPT chat on October 7, 2026. Which one you get depends on your plan, and answers can now come back as charts, forms and small working tools.
- First GPT-6 model
- GPT-6 Astra, September 3, 2026
- In the ChatGPT chat
- October 7 (paid plans), October 8 (Free and Go)
- Models
- Astra, Sol and Luna, plus GPT-6.1 Sol and Terra for developers
- New in the app
- Intelligent UI: answers with charts, forms and small tools
OpenAI shipped GPT-6 in three steps over five weeks. Astra came first, on September 3, in ChatGPT Work, Codex and the API. Sol and Luna followed on September 22 in the same places. The regular ChatGPT chat only switched on October 7 for paid plans and October 8 for Free and Go, so two people can both say they use GPT-6 and be talking about different models.
GPT-6 release dates
| Date | What shipped | Where |
|---|---|---|
| Sep 3, 2026 | GPT-6 Astra | ChatGPT Work and Codex on paid plans, and the API |
| Sep 22, 2026 | GPT-6 Sol and GPT-6 Luna | ChatGPT Work and Codex for Plus, Pro, Business, Enterprise and Edu, and the API. Free and Go users could try Luna in the desktop app. |
| Oct 7, 2026 | GPT-6 Sol with Intelligent UI | The ChatGPT chat for Plus, Pro, Business and Enterprise |
| Oct 8, 2026 | GPT-6 Luna | The ChatGPT chat for Free and Go |
| Late Oct 2026 | GPT-6.1 Sol and GPT-6.1 Terra | Listed in OpenAI's developer documentation |
If you only use ChatGPT for everyday questions, October 7 is the date that matters. Everything before it happened in Work, Codex and the API, which most people never open.
Which GPT-6 model you get in ChatGPT
| Plan | Model in the chat | Astra |
|---|---|---|
| Free | GPT-6 Luna | Not included |
| Go | GPT-6 Luna | Not included |
| Plus | GPT-6 Sol | Limited use in Work and Codex, extra credits available |
| Pro | GPT-6 Sol, with Astra listed as GPT-6 Pro | Work, Codex and the chat |
| Business and Enterprise | GPT-6 Sol, with Astra listed as GPT-6 Pro | Work, Codex and the chat |
OpenAI rolls models out gradually, and Enterprise admins decide when a workspace switches, so check the model menu in your own account if it doesn't match.
What Intelligent UI changes
Until now a ChatGPT answer was text, with the occasional table or code block. With GPT-6 the app picks a format for each question. OpenAI says answers "can include graphics, tappable buttons, forms, charts, and interactive experiences," so a comparison may come back side by side, or an explanation as a diagram you click through, while a quick question still gets a sentence or two.
ChatGPT can also build a small tool inside the chat, with inputs you can change. OpenAI's own examples are calculators, bill splitters and games. Prompts in that spirit to try:
- "Split a $186 dinner between five people, two of whom didn't drink."
- "How much would $300 a month grow to in 10 years at 6%? Let me change the rate."
- "Compare these three phone plans by total cost over two years."
- "Explain how a heat pump works, step by step."
GPT-6 also starts writing before it has finished reasoning and fills in the answer as it goes.
GPT-6 Sol vs Luna vs Astra vs Terra
| Model | What OpenAI says it's for | Where you'll meet it |
|---|---|---|
| Astra | "Our state-of-the-art, most powerful model." Long, multi-step work and software engineering. | Work and Codex; GPT-6 Pro in the chat on Pro, Business and Enterprise |
| Sol | Complex projects where cost matters | Default chat model on paid plans |
| Luna | "The most cost-efficient model" | Default chat model on Free and Go |
| Terra | Short writing from material you supply, computer use with a clear goal, small code fixes | GPT-6.1 Terra, for developers |
Astra, Sol and Luna are sizes within one generation, from largest to smallest. Two .1 updates, GPT-6.1 Sol and GPT-6.1 Terra, are already listed in OpenAI's developer docs.
How GPT-6 compares with Claude and Gemini
Labs choose which benchmarks they publish. Anthropic's announcement of Claude Opus 5.5 is one of the few that puts GPT-6 Astra next to its own model:
| Benchmark (Anthropic's numbers) | Claude Opus 5.5 | GPT-6 Astra |
|---|---|---|
| Terminal-Bench 4.0 (coding in a terminal) | 66.4% | 57.9% |
| AutomationBench | 40.0% | 41.4% |
| Terminal-Bench-Science 0.1 | 58.7% | 64.6% |
| Humanity's Last Exam, with tools | 67.7% | 57.2% |
Each model wins two of the four. Opus 5.5 leads by 8.5 points on Terminal-Bench 4.0 and 10.5 on Humanity's Last Exam; Astra leads by 5.9 on Terminal-Bench-Science and 1.4 on AutomationBench. Google makes its own claims for Gemini 4 Argon, on a different set of tests.
GPT-6 questions
When was GPT-6 released?
The first GPT-6 model, Astra, came out on September 3, 2026 in ChatGPT Work, Codex and the API. GPT-6 reached the regular ChatGPT chat on October 7, 2026 for paid plans and October 8 for Free and Go.
Is ChatGPT 6 out?
There's no app called ChatGPT 6. ChatGPT is the app, and GPT-6 is the family of models inside it. GPT-6 has been the default model in the ChatGPT chat since October 7, 2026 on paid plans and October 8 on Free and Go.
Is GPT-6 free?
Yes. Free accounts use GPT-6 Luna, the smallest model in the family. GPT-6 Sol needs a paid plan, and GPT-6 Astra is limited to paid plans in Work and Codex, or Pro and business plans in the chat.
What is GPT-6 Sol?
Sol is the mid-size GPT-6 model and the default in the ChatGPT chat on Plus, Pro, Business and Enterprise plans since October 7, 2026.
What is Intelligent UI in ChatGPT?
It's the GPT-6 feature that lets ChatGPT answer with charts, buttons, forms and small interactive tools, such as a calculator or bill splitter, when that suits the question better than text.
Is there a GPT-6 Pro?
Yes, as a name in the ChatGPT model menu. On Pro, Business and Enterprise plans, GPT-6 Astra appears in the chat as GPT-6 Pro.
Sources
- GPT-6 and Intelligent UI for everyone, OpenAI
- OpenAI brings GPT-6 to ChatGPT and debuts Intelligent UI, 9to5Mac, October 7, 2026
- GPT-6 Sol and Luna rollout post, OpenAI on X
- GPT-6 Astra is on ChatGPT Plus, but only in Work and Codex, Notebookcheck
- Model selection guide, OpenAI developer docs
- Introducing Claude Opus 5.5, Anthropic
- ChatGPT release notes, OpenAI Help Center