GPT-5.6 Terra vs GPT-6 Luna: pricing and benchmarks
GPT-6 Luna is 95% cheaper on input tokens ($0.10 vs $2.00 per 1M). GPT-6 Luna is 96% cheaper on output tokens ($0.50 vs $12.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-6 Luna costs $55.00 a month versus $1,160 for GPT-5.6 Terra, 95% less. Roughly tied. GPT-5.6 Terra scores 159.4 and GPT-6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
Which should you choose?
Roughly tied. GPT-5.6 Terra scores 159.4 and GPT-6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
GPT-5.6 Terra scores 86.0% on FrontierMath (Tiers 1–3) vs 78.9% for GPT-6 Luna.
GPT-6 Luna costs $0.20 per 1M tokens (3:1 input-to-output mix) vs $4.50 for GPT-5.6 Terra, 96% less.
GPT-6 Luna delivers statistically similar overall capability for 96% less.
Pricing and specs
| GPT-5.6 Terra | GPT-6 Luna | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| API model ID | gpt-5.6-terra | gpt-6-luna |
| Input / 1M tokens | $2.00 | $0.10 |
| Cached input / 1M tokens | $0.20 | $0.01 |
| Output / 1M tokens | $12.00 | $0.50 |
| Long-context rates | $4.00 in / $18.00 out on long-context requests | $0.20 in / $0.75 out on long-context requests |
| Context window | 1.05M tokens | 1.05M tokens |
| Max output | 128K tokens | 128K tokens |
| Batch discount | 50% off | 50% off |
Benchmarks
| GPT-5.6 Terra | GPT-6 Luna | |
|---|---|---|
| Epoch Capabilities Index | 159.4 | 156.3 |
| GPQA Diamond· Science reasoning | 93.3% | 90.5% |
| FrontierMath (Tiers 1–3)· Advanced math | 86.0% | 78.9% |
| SimpleQA Verified· Factual accuracy | 43.2% | 41.4% |
| ARC-AGI-2· Abstract reasoning | 83.9% | 59.3% |
| DeepSWE· Coding | 69.6% | — |
| APEX-Agents· Agentic work | 58.2% | 44.3% |
Source: Epoch AI, best recorded result per model (CC BY 4.0). A dash means no published score. See all benchmarks
Monthly cost for real workloads
| Workload | GPT-5.6 Terra | GPT-6 Luna | Difference |
|---|---|---|---|
Support chatbot 100,000 replies a month, ~1,500 input tokens (system prompt + history) and ~400 output tokens each. | $780.00 | $35.00 | GPT-6 Luna 96% cheaper |
Document Q&A (RAG) 50,000 questions a month with ~8,000 tokens of retrieved context and ~600 output tokens each. | $1,160 | $55.00 | GPT-6 Luna 95% cheaper |
Coding agent 10,000 agent steps a month, ~40,000 input tokens each (70% read from the prompt cache) and ~2,000 output tokens. | $536.00 | $24.80 | GPT-6 Luna 95% cheaper |
Cached chatbot The same 100,000-reply support chatbot, but 60% of each prompt (system prompt + conversation history) is served from the prompt cache. | $618.00 | $26.90 | GPT-6 Luna 96% cheaper |
Meeting notes 10,000 meetings a month summarized from ~12,000-token transcripts, ~1,000 output tokens each. | $360.00 | $17.00 | GPT-6 Luna 95% cheaper |
Bulk translation 200,000 short translations a month, ~800 input and ~800 output tokens each. | $2,240 | $96.00 | GPT-6 Luna 96% cheaper |
Content moderation 1,000,000 classifications a month, ~400 input tokens and ~80 output tokens each. | $1,760 | $80.00 | GPT-6 Luna 95% cheaper |
Article drafting 300 long-form articles a month written from a ~4,000-token brief and outline, ~5,000 output tokens each. | $20.40 | $0.87 | GPT-6 Luna 96% cheaper |
Code review bot 30,000 pull-request reviews a month, ~5,000 input tokens each (30% cached repository context) and ~700 output tokens. | $471.00 | $21.45 | GPT-6 Luna 95% cheaper |
Invoice extraction 100,000 documents a month parsed into structured JSON, ~1,200 input and ~250 output tokens each. | $540.00 | $24.50 | GPT-6 Luna 95% cheaper |
Estimates use standard list prices and ignore cache-write surcharges. Different tokenizers can count the same text differently, so test with your own prompts.
GPT-5.6 Terra vs GPT-6 Luna cost calculator
- $55.00/mo$0.0011 / req
- GPT-5.6 TerraOpenAI$1,160/mo$0.02 / req
Standard-tier list prices. Long-context rates apply automatically where the provider publishes a threshold. Excludes cache-write surcharges, taxes, batch and volume discounts.
GPT-5.6 Terra pricing notes
The GPT-5.6 model that balances intelligence and cost.
- Cache writes are billed at $2.50 per 1M tokens.
- Fast mode costs 2x the standard rate; Flex costs half.
GPT-6 Luna pricing notes
OpenAI’s most efficient GPT-6 model, for focused, high-volume tasks.
- Cache writes are billed at $0.125 per 1M tokens.
- Fast mode costs 2x the standard rate; Flex costs half.
- Regional (data residency) endpoints add a 10% uplift, and EU data residency is available only with standard processing.
Frequently asked questions
- Is GPT-5.6 Terra cheaper than GPT-6 Luna?
- GPT-6 Luna is 95% cheaper on input tokens ($0.10 vs $2.00 per 1M). GPT-6 Luna is 96% cheaper on output tokens ($0.50 vs $12.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-6 Luna costs $55.00 a month versus $1,160 for GPT-5.6 Terra, 95% less.
- Which is more capable, GPT-5.6 Terra or GPT-6 Luna?
- Roughly tied. GPT-5.6 Terra scores 159.4 and GPT-6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
- How much does GPT-5.6 Terra cost per 1M tokens?
- GPT-5.6 Terra costs $2.00 per 1M input tokens and $12.00 per 1M output tokens, and $0.20 per 1M cached input tokens on OpenAI’s standard tier.
- How much does GPT-6 Luna cost per 1M tokens?
- GPT-6 Luna costs $0.10 per 1M input tokens and $0.50 per 1M output tokens, and $0.01 per 1M cached input tokens on OpenAI’s standard tier.
- Which has the larger context window, GPT-5.6 Terra or GPT-6 Luna?
- Both offer a 1.05M-token context window.