GPT-5.6
GPT-5.6 is OpenAI's generally available model family for ChatGPT, Codex, and the API, with Sol for frontier work, Terra for balanced intelligence and cost, and Luna for high-volume cost-sensitive workloads. OpenAI's current API pages list Sol at $4 input, $0.40 cached input, and $20 output per 1 million tokens during a promotion running through at least November 21, 2026.
GPT-5.6 turns one family into three durable capability tiers with a shared 1,050,000-token context window and materially different prices. OpenAI reduced Luna and Terra prices on July 30, then reduced Sol input by 20% and output by 33% on August 21 for at least three months. A July 2026 mathematics paper gives a separate example of Sol contributing a construction idea that human authors then verified and turned into a proof.
OpenAI moved GPT-5.6 from limited preview to general availability on July 9, 2026. The current launch post and Sol model page now list a temporary Sol reduction to $4 input, $0.40 cached input, and $20 output per 1 million tokens through at least November 21, while Terra remains $2/$0.20/$12 and Luna remains $0.20/$0.02/$1.20. Provider-specific promotions can stack differently and do not replace OpenAI's direct rates. A July 29 arXiv paper says Sol suggested a Maxwell-conjecture counterexample construction that the human authors then verified and proved.
- Escalating difficult software engineering tasks to GPT-5.6 Sol.
- Routing balanced everyday coding and knowledge work to GPT-5.6 Terra.
- Using GPT-5.6 Luna for cost-sensitive, high-volume workloads.
- Exploring hard mathematical constructions with human proof, verification, and computer-algebra checks.
- Comparing cached-input and long-context costs before production routing.
OpenAI describes GPT-5.6 as a generally available family with durable capability tiers. Sol is the frontier model, Terra balances intelligence and cost, and Luna is optimized for cost-sensitive high-volume work. The official API model IDs are gpt-5.6-sol, gpt-5.6-terra, and gpt-5.6-luna; the gpt-5.6 alias routes to Sol.
- Sol currently costs $4 input, $0.40 cached input, and $20 output per 1 million tokens through at least November 21, 2026.
- Terra currently costs $2 input, $0.20 cached input, and $12 output per 1 million tokens.
- Luna currently costs $0.20 input, $0.02 cached input, and $1.20 output per 1 million tokens.
OpenAI cut Terra pricing by 20% and Luna pricing by 80% on July 30. On August 21 it also reduced Sol from $5 input and $30 output to $4 input and $20 output per 1 million tokens, with cached input moving from $0.50 to $0.40. OpenAI says the Sol rates are promotional through at least November 21, so budget owners should recheck the direct model page after that date.
The primary paper disproves the Maxwell conjecture by exhibiting a five-charge configuration with at least 24 non-degenerate critical points. Its acknowledgement says GPT-5.6 Sol suggested the idea for the construction, while Philip Arathoon, Gavin Ball, and Matthew D. Kvalheim verified the mathematics and wrote the proof. Mathematica and Maple supported calculations and visualization. The defensible claim is model-assisted discovery, not that GPT-5.6 Sol independently proved the theorem.
Choose Sol for complex professional work where quality and frontier reasoning justify the price. Choose Terra when intelligence and cost need to stay balanced, and Luna for high-volume or cost-sensitive workloads. Validate the three tiers with the same harness because a lower-priced model that completes the task reliably can be the better production route.
Cached input is priced at 10% of ordinary input, while cache writes cost 1.25 times the uncached input rate. Requests above 272,000 input tokens are charged at twice the input rate and 1.5 times the output rate for the full request, so the advertised base price is not the whole cost model for very long prompts.
The September 2026 successor for the hardest end-to-end work, now available through eligible ChatGPT plans and Codex surfaces.
The earlier OpenAI frontier-model page used as a coding and professional-work comparison anchor.
Anthropic high-end model for complex reasoning and coding-heavy autonomy work.
Z.AI long-context reasoning model that users may compare for coding and engineering workflows.
Source confidence
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GPT-5.6 FAQ
Common questions about GPT-5.6.
Is GPT-5.6 generally available?+
Yes. OpenAI launched GPT-5.6 for general availability on July 9, 2026 across ChatGPT, Codex, and the OpenAI API, with product access still varying by plan and rollout surface.
Which GPT-5.6 model should I try first?+
Use Sol for the hardest professional and coding work, Terra when you need a balance of intelligence and cost, and Luna for high-volume or cost-sensitive workloads. Test the same task across tiers before choosing a default.
How much does GPT-5.6 cost in the API?+
Per 1 million tokens, Sol currently costs $4 input and $20 output, Terra costs $2 input and $12 output, and Luna costs $0.20 input and $1.20 output. Cached input costs $0.40 for Sol, $0.20 for Terra, and $0.02 for Luna. Sol's direct rates are promotional through at least November 21, 2026; provider-specific discounts, cache writes, and prompts above 272,000 input tokens have separate pricing.
How much did GPT-5.6 Terra and Luna pricing drop?+
OpenAI's July 30 update says GPT-5.6 Terra pricing fell by 20% and Luna pricing by 80% from their July 9 launch levels. Terra input moved from $2.50 to $2 and output from $15 to $12; Luna input moved from $1 to $0.20 and output from $6 to $1.20 per 1 million tokens, with cached-input rates moving in the same proportions.
Did GPT-5.6 Sol disprove the Maxwell conjecture by itself?+
No. The paper authors acknowledge that GPT-5.6 Sol suggested the construction idea, but they verified the mathematics and wrote the proof, with computer algebra used for calculations and visualization. Describe it as model-assisted mathematical discovery rather than an autonomous proof.