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 Luna model page lists $0.20 input, $0.02 cached input, and $1.20 output per 1 million tokens.
GPT-5.6 turns one family into three durable capability tiers with a shared 1,050,000-token context window and materially different prices. Luna's current rates are 80% below its July 9 launch prices, while a July 2026 mathematics paper gives a concrete 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 across ChatGPT, Codex, and the API. The launch announcement priced Luna at $1 input and $6 output per 1 million tokens, while the current Luna API model page lists $0.20 input, $0.02 cached input, and $1.20 output. That is an 80% reduction across all three token rates, although OpenAI has not published a separate effective-date announcement. A July 29 arXiv paper titled “The Maxwell Conjecture is False” acknowledges that GPT-5.6 Sol suggested the counterexample construction; the authors say they verified the mathematics and wrote the argument, with computer algebra used for calculations and visualization. That is evidence of assisted mathematical discovery, not an autonomous model proof.
- 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 costs $5 input, $0.50 cached input, and $30 output per 1 million tokens.
- Terra costs $2.50 input, $0.25 cached input, and $15 output per 1 million tokens.
- Luna currently costs $0.20 input, $0.02 cached input, and $1.20 output per 1 million tokens.
OpenAI's July 9 GPT-5.6 launch announcement listed Luna at $1 input and $6 output per 1 million tokens, with cached input at $0.10 under the 90% cache-read discount. The live Luna API model page now lists $0.20 input, $0.02 cached input, and $1.20 output. Each rate is 80% lower; OpenAI has not published a separate announcement that names the exact effective 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.
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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 costs $5 input and $30 output, Terra costs $2.50 input and $15 output, and Luna now costs $0.20 input and $1.20 output. Luna cached input costs $0.02; cache writes cost 1.25 times the uncached input rate, and prompts above 272,000 input tokens use higher long-context rates.
How much did GPT-5.6 Luna pricing drop?+
GPT-5.6 Luna's current API rates are 80% below its July 9 launch prices. Input fell from $1 to $0.20, cached input from $0.10 to $0.02, and output from $6 to $1.20 per 1 million tokens. OpenAI's live model page confirms the new rates, but no separate announcement gives an exact effective date.
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.