By GPT-6 Astra vs Sol vs Luna in ChatGPT
Astra now ranks above Sol, so older guides name the wrong best model. Here is what each GPT-6 tier is for in ChatGPT and what the same models cost in the API.
The short answer
GPT-6 Astra vs Sol vs Luna is a question about tiers. Astra is the top model in the GPT-6 family. Sol is the middle tier. Luna is the low-cost tier. OpenAI's own latest-model guide for developers uses exactly those positions: it labels Astra "Highest intelligence", GPT-6.1 Sol "Balanced speed, cost, and intelligence", and Luna "Fastest and most cost-effective". OpenAI's API models page words it differently but keeps the same order. It calls Astra "Our most capable model for the most demanding work." and Luna "Our most efficient model for focused, high-volume tasks."
GPT-6 is now in ChatGPT. OpenAI's deployment safety page for the October release, published October 7, 2026, says: "We're launching GPT-6 to everyone in ChatGPT, across free and paid plans globally." The same page says the new Sol and Luna "will replace GPT-5.6 Sol and GPT-5.6 Luna in ChatGPT."
This guide is for people who use ChatGPT in the chat window. It explains what each tier is for and which plan gets which model. It also gives the price of the same models in the API (application programming interface, the paid developer service). Where OpenAI has not confirmed something on a page we could open, the guide says so.
Why older guides call Sol the best model
The name "Sol" has belonged to more than one model. Before this release, ChatGPT ran GPT-5.6 Sol and GPT-5.6 Luna. OpenAI's safety page for Astra calls it "the most capable model we have ever broadly deployed", and it compares Astra mainly against GPT-5.6 Sol. So a guide written for the GPT-5.6 lineup that calls Sol the best OpenAI model is describing a lineup that is now being replaced. In GPT-6, Astra sits above Sol.
The second trap is timing. Some guides from late September 2026 say Sol and Luna are not in ChatGPT yet. The October 7 safety page says GPT-6 launches to everyone in ChatGPT, so those guides are out of date. Check the date on any guide before you trust its ranking.
The third trap is the version number. GPT-5.6 Sol, GPT-6 Sol and GPT-6.1 Sol are three separate models. When you read a claim about "Sol", look for the version. Without it, the claim could be about any of them.
What is each GPT-6 tier built for?
OpenAI's latest-model guide describes each tier in one line. These are OpenAI's words, quoted directly:
- GPT-6 Astra: "For the most demanding reasoning, coding, and professional work."
- GPT-6.1 Sol: "Near-Astra performance for complex work at a lower cost."
- GPT-6 Luna: "Strong performance for focused, high-volume tasks."
In practice, pick the tier by the size of the job. Long reasoning and hard code are what Astra is for. Everyday writing and most coding questions are Sol's job. Short, repeated tasks such as sorting messages or rewriting a sentence fit Luna, because Luna is the fastest and the cheapest tier.
OpenAI's model page for Astra lists a context window (the amount of text the model can read in one request) of 1,050,000 tokens, a maximum output of 128K tokens, and a knowledge cutoff of April 30, 2026. A token is a piece of a word, and API prices are counted in tokens.
Which GPT-6 model does my ChatGPT plan use?
This is the question most chat users have. OpenAI answers it in the ChatGPT release notes in its help center, checked on October 13, 2026. The October 7 entry says: "Plus, Pro, Business, and Enterprise use GPT-6 Sol; Free and Go use GPT-6 Luna." In short:
- Free and Go plans use Luna.
- Plus, Pro, Business and Enterprise use Sol in the chat window.
- The "Pro" reasoning option on the Pro plan runs on Astra.
The same entry says the rollout started on October 7 in the Chat tab for Plus, Pro, Business and Enterprise, and reached Free and Go the next day. For Enterprise, availability depends on admin settings. The October 7 safety page does not give a per-plan list. It only says GPT-6 reaches free and paid plans, and that the new Sol and Luna replace the GPT-5.6 versions. To check what your own account uses today, open the model menu in ChatGPT.
If you are on a free plan and also wonder about ads, that depends on the plan too, and it is covered in which ChatGPT plans show ads.
Codex and ChatGPT Work still run earlier versions
The new models did not reach every OpenAI product on the same day. The October 7 safety page says: "Users accessing GPT-6 Sol and GPT-6 Luna in Codex, and via ChatGPT Work, are still using previously released versions." The ChatGPT release notes say the same: the models behind Work and Codex did not change with this release.
So the model called Sol in the chat window and the model called Sol in Codex are not the same build right now. If a result in Codex differs from a result in chat, this is one reason. If you run Codex through your ChatGPT plan, using Codex with a ChatGPT subscription explains how that setup works.
GPT-6 API prices for Astra, Sol and Luna
ChatGPT plans have a monthly price. The API charges per token instead. These are the standard-tier list prices on OpenAI's API pricing page, checked on October 13, 2026. All prices are in US dollars per 1 million tokens, for prompts of 272K input tokens or fewer.
The data behind this chart
[
{
"label": "gpt-6-astra",
"input_usd": "10.00",
"cached_input_usd": "1.00",
"cache_write_usd": "12.50",
"output_usd": "50.00"
},
{
"label": "gpt-6.1-sol",
"input_usd": "2.00",
"cached_input_usd": "0.10",
"cache_write_usd": "2.50",
"output_usd": "10.00"
},
{
"label": "gpt-6-sol",
"input_usd": "2.00",
"cached_input_usd": "0.20",
"cache_write_usd": "2.50",
"output_usd": "10.00"
},
{
"label": "gpt-6-luna",
"input_usd": "0.10",
"cached_input_usd": "0.01",
"cache_write_usd": "0.125",
"output_usd": "0.50"
}
]Astra costs $10.00 per million input tokens and $50.00 per million output tokens. Luna costs $0.10 for input and $0.50 for output. Both Sol models sit between them at $2.00 for input and $10.00 for output.
Output tokens cost five times as much as input tokens on every model in the table. That matters because a model that writes long answers costs more than one that only reads long prompts.
Cached input is the lower price for input the API has already seen in a recent request, such as a long system prompt that repeats. Cache writes are the price for storing that input the first time. The pricing page also lists Batch, Flex, Fast and Ultrafast tiers with different rates. This guide covers only the standard tier.
Why does the API list two Sol models?
The API has both gpt-6-sol and gpt-6.1-sol. Their input and output prices are the same. The difference in the table is cached input: GPT-6.1 Sol charges $0.10 per million cached tokens, and GPT-6 Sol charges $0.20.
OpenAI's latest-model guide names GPT-6.1 Sol as the balanced tier. It mentions gpt-6-sol only for developers who already use it: "If you already use gpt-6-sol, review the migration guidance before switching to GPT-6.1 Sol." The guide also says gpt-6-sol supports a reasoning effort of none, which GPT-6 Astra and GPT-6.1 Sol do not.
For chat users, the safety page and the ChatGPT release notes both name GPT-6 Sol for ChatGPT, not GPT-6.1 Sol. So do not assume the chat window runs the 6.1 build.
What does one request cost on each model?
Per-million prices are hard to picture. This chart applies the short-context prices above to one example request: 10,000 input tokens and 1,000 output tokens, with no caching. That is roughly a long document plus a one-page answer. The figures are our arithmetic from OpenAI's list prices, not a number OpenAI publishes.
The data behind this chart
[
{
"label": "gpt-6-astra",
"input_cost_usd": "0.10",
"output_cost_usd": "0.05",
"total_usd": "0.15"
},
{
"label": "gpt-6.1-sol",
"input_cost_usd": "0.02",
"output_cost_usd": "0.01",
"total_usd": "0.03"
},
{
"label": "gpt-6-sol",
"input_cost_usd": "0.02",
"output_cost_usd": "0.01",
"total_usd": "0.03"
},
{
"label": "gpt-6-luna",
"input_cost_usd": "0.001",
"output_cost_usd": "0.0005",
"total_usd": "0.0015"
}
]The request costs $0.15 on Astra, $0.03 on Sol and $0.0015 on Luna. One request is cheap on any of them. The gap matters at volume: a script that sends the same request thousands of times a day pays for every one of them, so the tier choice decides most of the bill.
Prompts over 272K tokens cost more
The pricing page defines two bands: "Short context: ≤272K input tokens. Long context: >272K input tokens." Above that line, a higher price applies. For Astra, OpenAI's model page words it this way: "Prompts with more than 272K input tokens are priced at 2x input and cache rates and 1.5x output for the full request." The key words are "the full request". The higher rate then covers every token in that request, including the first 272K.
The data behind this chart
[
{
"label": "gpt-6-astra",
"input_usd": "20.00",
"cached_input_usd": "2.00",
"cache_write_usd": "25.00",
"output_usd": "75.00"
},
{
"label": "gpt-6.1-sol",
"input_usd": "4.00",
"cached_input_usd": "0.20",
"cache_write_usd": "5.00",
"output_usd": "15.00"
},
{
"label": "gpt-6-sol",
"input_usd": "4.00",
"cached_input_usd": "0.40",
"cache_write_usd": "5.00",
"output_usd": "15.00"
},
{
"label": "gpt-6-luna",
"input_usd": "0.20",
"cached_input_usd": "0.02",
"cache_write_usd": "0.25",
"output_usd": "0.75"
}
]In the long band, Astra input rises to $20.00 and output to $75.00. The table shows the same pattern for Sol and Luna: input doubles and output rises by half. This is an API pricing rule. The pricing page does not say how ChatGPT plans handle very long conversations.
Does a ChatGPT subscription include API access?
This question comes up often, and the honest answer is short. We did not find an OpenAI page that says a ChatGPT plan includes API usage. We also did not find one that says it excludes it. So this guide does not claim either.
Here is what OpenAI does state. The API pricing page bills per token: "Tokens are billed at the chosen model's input and output rates." It also lists a model called chat-latest under a ChatGPT heading, with its own per-token API price. That is an API model with an API price. It is not a description of a ChatGPT plan. For OpenAI models used through cloud platforms, the page says they "are billed through those services", naming Amazon Bedrock and Microsoft Azure.
If you plan to call the API, budget from the per-token prices above. For the current answer on plans and the API, check OpenAI's help center before you pay for either.
What about message limits and the Pro plan?
This guide does not quote message caps for Astra, Sol or Luna in ChatGPT. We could not open an OpenAI page that publishes them, and secondhand figures go out of date quickly.
Pro plan usage is changing, and OpenAI has now confirmed it. A September 29, 2026 entry in the ChatGPT release notes introduces a Pro 500 plan at $500 a month, which has the most included usage of the Pro plans. Another entry the same day says Pro 200 is open to new subscribers again at $200 a month, that its included usage allowances are changing, and that affected users will get an email. The entries do not give the new limits as numbers. If usage limits are your reason to choose Pro, read the limits in OpenAI's help center on the day you subscribe. For a plan-level comparison with Anthropic's top consumer plan, see Claude Max vs ChatGPT Pro.
How does GPT-6 compare with Claude on cost?
If you also pay for Claude, the useful comparison is cost. For the per-token side, Claude vs ChatGPT API pricing compares the two APIs. For the monthly side, what a Claude or ChatGPT subscription costs compares the paid plans, and the free plans of Claude, ChatGPT and Gemini covers what you get without paying.
FAQ
Is GPT-6 Sol better than GPT-6 Astra?
No. In the GPT-6 family, Astra is the top tier. OpenAI's latest-model guide labels Astra "Highest intelligence" and GPT-6.1 Sol "Balanced speed, cost, and intelligence". Guides that call Sol the best OpenAI model were usually written for the GPT-5.6 lineup, which GPT-6 is replacing in ChatGPT from October 2026. Sol is the better choice when you want lower cost and faster answers for everyday work.
Which GPT-6 model do free ChatGPT users get?
Free and Go plans use GPT-6 Luna. OpenAI's ChatGPT release notes for October 7, 2026 say Plus, Pro, Business and Enterprise use GPT-6 Sol, and Free and Go use GPT-6 Luna. Free and Go users got it one day after the paid plans. Check the model menu in your ChatGPT app to see what your account uses today.
Why does Codex give different answers from ChatGPT with the same model name?
They may not be the same build. OpenAI's October 7, 2026 safety page says users of GPT-6 Sol and GPT-6 Luna in Codex and in ChatGPT Work "are still using previously released versions." So Sol in Codex and Sol in the chat window can differ for now.
How much does GPT-6 cost in the API?
At standard list prices for prompts up to 272K input tokens, Astra costs $10.00 per million input tokens and $50.00 per million output tokens. Both Sol models cost $2.00 and $10.00. Luna costs $0.10 and $0.50. Prompts above 272K input tokens are billed at higher long-context rates for the whole request. OpenAI's API pricing page has the current figures.
Does ChatGPT Plus include OpenAI API credits?
We found no OpenAI page that says a ChatGPT plan includes API usage, and none that says it excludes it. The API pricing page bills per token at each model's input and output rates and does not describe ChatGPT plans. Check OpenAI's help center for the current answer before you rely on either.