GPT-6 Sol vs Astra comes down to one trade-off: Astra is OpenAI's most capable model and costs five times as much per token, while GPT-6.1 Sol gets close to Astra on coding, computer use and professional work at a fraction of the price. GPT-6 Luna is the fast, very cheap option for everyday and high-volume tasks. For most people and most apps, GPT-6.1 Sol is the sensible default, with Astra reserved for the hardest problems.
Here is how the names fit together, what each model costs, and where you can actually use it, as of October 5, 2026.
How OpenAI names its models now
OpenAI changed its naming scheme with GPT-5.6 in July 2026. In that launch post, OpenAI explained that "the number identifies the generation, while Sol, Terra, and Luna are durable capability tiers that can advance on their own cadence." Sol was the flagship tier, Terra the balanced middle, and Luna the fastest and cheapest, per OpenAI's GPT-5.6 announcement.
GPT-6 added a new tier above Sol. Astra arrived on September 3, 2026, as OpenAI's new top model. GPT-6 Sol and GPT-6 Luna followed on September 22, and GPT-6.1 Sol replaced GPT-6 Sol as the recommended mid-tier model just a week later, on September 29. OpenAI has not announced a GPT-6 Terra.
That cadence is why the names confuse people: the tier tells you roughly how capable and expensive a model is, and the number tells you which generation it belongs to. A GPT-6.1 Sol is a newer, better Sol, not a different product.
GPT-6 Sol vs Astra vs Luna at a glance
| Model | Role | API price per million tokens (input / output) | API ID |
|---|---|---|---|
| GPT-6 Astra | Most capable, best results | $10 / $50 | gpt-6-astra |
| GPT-6.1 Sol | Near-Astra intelligence, everyday flagship | $2 / $10 (cached input $0.10) | gpt-6.1-sol |
| GPT-6 Sol | Previous Sol, superseded by 6.1 | $2 / $10 | gpt-6-sol |
| GPT-6 Luna | Fast, efficient, high volume | $0.10 / $0.50 | gpt-6-luna |
In words: Astra costs ten dollars per million input tokens and fifty per million output tokens. Both Sol models cost two dollars in and ten out, and GPT-6.1 Sol's cached input costs just ten cents per million. Luna costs ten cents in and fifty cents out, a hundredth of Astra's price. OpenAI's GPT-6 Sol and Luna post notes that the Sol and Luna prices are half of what GPT-5.6 Sol and Luna cost under their promotional pricing.
Astra also has a Fast mode in the API that delivers up to twice the speed at twice the standard price. OpenAI says a GPT-6.1 Sol Ultrafast option with up to eight times faster generation in Codex is coming.
GPT-6 Astra: when only the best will do
Astra is the model OpenAI recommends when "you want the best results and an uncompromising experience." It leads OpenAI's tables on computer use, agentic coding, scientific workflows and math, and OpenAI says it was its largest training run yet. It is also the first model OpenAI has classed as Critical in cybersecurity, so it refuses some advanced security tasks for ordinary users, as covered in our GPT-6 Astra vs Claude Fable 5.1 comparison.
Pros: top capability, Astra Pro variant on higher plans, Fast and Ultrafast options. Cons: five times Sol's token price, refusals on advanced cyber work, and OpenAI says its reasoning is harder to monitor than earlier models'.
One more detail: there will not be a GPT-6.1 Astra for now. OpenAI pulled the planned model after it missed the company's safety bar on staying within scope and accurately describing its own work, as the BBC reported. GPT-6 Astra remains available.
GPT-6.1 Sol: the default for most work
According to OpenAI's GPT-6.1 Sol post, 6.1 Sol matches Astra on the DeepSWE software-engineering benchmark at roughly one-fifth of the cost, and comes within about two points of Astra on the OSWorld computer-use test at roughly one-seventh the cost per task. On scientific workflows at maximum effort, OpenAI puts its average cost at $5.47 per task, against $23.80 for Astra, though Astra still scores highest there.
OpenAI also reports fewer factual errors: at low reasoning effort, the share of responses containing a factual error on a deliberately difficult test set fell from 11.4 percent for GPT-6 Sol to 7.7 percent.
Pros: near-Astra results for many tasks, cheap cached input, available on Plus and higher plans in ChatGPT Work and Codex. Cons: still behind Astra on the hardest scientific and computer-use tasks; not yet in ChatGPT's regular Chat mode.
GPT-6 Luna: cheap and fast
Luna is built for high-volume, latency-sensitive work: classification, extraction, routine drafting, and simple coding. OpenAI says GPT-6 Luna at higher effort matches GPT-5.6 Sol on its factuality evaluation at about a hundredth of the cost. It is also the model free and Go users can reach in the ChatGPT desktop app.
Pros: extremely low price, fast, good enough for most routine tasks. Cons: noticeably weaker on long, complex agentic work.
Which GPT-6 model you get in ChatGPT
ChatGPT now has two main modes: Chat, for conversation, and Work, an agent for longer tasks. The newest models land in Work and Codex first.
- GPT-6 Astra: rolling out to Plus, Pro, Business and Enterprise. Pro, Business and Enterprise also get Astra Pro. Enterprise admins must switch Astra on for their workspace.
- GPT-6.1 Sol: in ChatGPT Work and Codex for Plus, Pro, Business, Enterprise and Edu. OpenAI says it is "not yet available in Chat."
- GPT-6 Luna: in Work and Codex for paid plans, and in the desktop app for Free and Go users.
OpenAI's plans are Free, Go at $8 a month, Plus at $20, and three Pro tiers at $100, $200 and $500. The $500 Pro tier, added on September 29, is the only one that unlocks Astra Ultrafast, according to OpenAI's release notes. For a plan-by-plan comparison with Claude and Gemini, see our ChatGPT vs Claude vs Gemini vs Grok guide.
How to choose
- Start with GPT-6.1 Sol for coding, documents, analysis and agents. It is the best balance of cost and capability in OpenAI's lineup.
- Escalate to Astra when 6.1 Sol fails your own tests: hard scientific workflows, long computer-use tasks, or work where a better first attempt saves expensive human time.
- Drop to Luna for bulk, simple or real-time tasks where cost and speed dominate.
- Compare across labs before committing. Claude Opus 5.5 at $4 and $20 per million tokens and Gemini's Flash models are strong alternatives; see Claude Fable vs Opus vs Mythos and our tool pages for Claude and Gemini.
If you build on the OpenAI API, use explicit model IDs rather than relying on the ChatGPT picker, and check OpenAI's models page for deprecation dates now that 6.1 Sol has superseded 6 Sol. Everyday users of ChatGPT mostly just need to know that Work gets new models before Chat.
FAQ
Is GPT-6 Sol better than GPT-6 Astra?
No. Astra is OpenAI's most capable model. GPT-6.1 Sol comes close on many coding and professional tasks at about one-fifth of Astra's token price, which is why it is the better value for most work.
What is the difference between GPT-6 Sol and GPT-6.1 Sol?
GPT-6.1 Sol is an upgrade released a week after GPT-6 Sol. It costs the same per token, halves the cached-input price to $0.10 per million tokens, and scores higher on coding, computer use, science and factuality, according to OpenAI.
What happened to GPT Terra?
Terra was the balanced middle tier in the GPT-5.6 family. OpenAI has not released a GPT-6 Terra; the GPT-6 family so far consists of Astra, Sol and Luna.
Can free ChatGPT users use GPT-6?
Free and Go users can use GPT-6 Luna in the ChatGPT desktop app. Astra and GPT-6.1 Sol require a paid plan.
How much does GPT-6 Astra cost?
Through the API, $10 per million input tokens and $50 per million output tokens, with Fast mode at twice those rates. In ChatGPT, Astra is included in Plus, Pro, Business and Enterprise allowances, with credits available for extra usage.