GPT-6 Sol and Luna
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GPT-6 Sol: API prices cut in half for coding and agents, Luna goes even lower
Updated on September 27, 2026
GPT-6 Sol is the mid-tier model in OpenAI's GPT-6 generation, built for coding, agents and complex work tasks. It arrived on September 22, 2026, alongside the smaller GPT-6 Luna, roughly 90 minutes after Claude Opus 5.5. API rates land at $2 per million input tokens and $10 for output, half of what the 5.6 generation charged. Free and Go accounts even get Luna in the desktop app.
Pros
- API rates cut in half versus the 5.6 generation
- Astra-level reliability, according to OpenAI
- 1,050,000-token context window
- Luna open to free accounts via the desktop app
Cons
- Not yet available in regular Chat
- Long prompts over 272K tokens cost extra
- Documentation and benchmarks published by OpenAI alone so far
GPT-6, a three-tier family, Astra, Sol and Luna
OpenAI's GPT-6 family counts three models, the top-end Astra released in early September 2026, the mid-tier Sol and the lightweight Luna. The lab founded in 2015 trained Sol and Luna with methods similar to Astra's, carrying over its work on factuality, coding and computer use.
According to OpenAI, Sol makes about half as many mistakes as GPT-5.6 Sol on internal factuality tests, and posts 33.2% on AutomationBench at xhigh effort for $0.27 per task, plus 68.8% on the DeepSWE v1.1 coding benchmark. In practice, the gpt-6-sol API model takes text and images across a 1,050,000-token context window.
| Model | Role in the family | Typical tasks |
|---|---|---|
| GPT-6 Astra | Top-end model | Deep analysis, research, science |
| GPT-6 Sol | Mid-tier for code and agents | Development, debugging, business automation |
| GPT-6 Luna | Light and fast | Summaries, extraction, quick answers |
Sol and Opus 5.5 put to the test on real coding builds
A first look at OpenAI's Sol and Luna release
GPT-6 Luna, the small model for high-volume work
GPT-6 Luna aims at high-volume tasks with a clear goal. Hand it 500 support tickets to sort and it gets through them for pennies. At high effort, it gains 5.4 points on AutomationBench over its predecessor at a 58% lower cost per task, again per OpenAI's own figures.
There is a nice twist for anyone on a free plan, since Luna ships to Free and Go accounts in the ChatGPT desktop app, while Sol stays with paid plans in Work and Codex, plus the API for everyone.
- Document summaries at scale
- Structured information extraction
- Quick answers and classification
Prices halved, 90 minutes after Claude Opus 5.5
GPT-6 Sol costs $2 per million input tokens and $10 for output, against $4 and $20 for its predecessor, while Luna drops to $0.10 and $0.50. Cached input reads get a 90% discount, $0.20 on Sol, and prompts above 272K input tokens are billed at twice the input rate and 1.5x on output. Rates do drift over time, so treat OpenAI's pricing page as the final word.
Timing added some spice, as Anthropic shipped Claude Opus 5.5 about 90 minutes earlier at $4 and $20. Independent readings from Artificial Analysis and the LLM leaderboard rankings will show over the coming weeks where Sol really lands. In this race between large language models, cost per task has become the referee, and that is Sol's home turf.
Frequently asked questions
What is GPT-6 Sol?
GPT-6 Sol is the mid-tier model in OpenAI's GPT-6 generation, sitting below the top-end Astra and above the lightweight Luna. It targets coding, agents and complex work, priced at $2 per million input tokens and $10 for output. You can reach it through Codex, ChatGPT Work and the API under the id gpt-6-sol.
When was GPT-6 released?
Early September 2026 for GPT-6 Astra, then September 22, 2026 for GPT-6 Sol and GPT-6 Luna. No model is called plain GPT-6, since the generation splits into three tiers named after celestial bodies, and the ChatGPT rollout happened gradually, with regular Chat not served on day one.
What is the difference between GPT-6 Sol and Luna?
Sol reasons harder and aims at coding, agents and analysis, while Luna favors speed and bulk jobs such as summaries, extraction and classification. Twenty times cheaper on input, Luna is also the only one of the pair open to free accounts, through the desktop app. Sol lists a knowledge cutoff of April 20, 2026.
GPT-6 Sol vs Claude Opus 5.5, which one should you pick?
Budget and volume decide it. Sol costs half as much per million tokens, while Anthropic highlights Opus 5.5 on agentic coding and computer use, and the two companies do not publish the same benchmarks. For agents running around the clock or bulk coding, Sol wins on the bill.
Verdict: Developers and teams running agents all day walk away with a lighter bill and Astra-grade reliability, and ChatGPT subscribers find it in Work and Codex; when a gnarly problem calls for the top score, Astra sits one menu away in the same account.
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