Gemini 3.5 Flash vs GPT-5.6 Luna: pricing and benchmarks
GPT-5.6 Luna is 87% cheaper on input tokens ($0.20 vs $1.50 per 1M). GPT-5.6 Luna is 87% cheaper on output tokens ($1.20 vs $9.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-5.6 Luna costs $116.00 a month versus $870.00 for Gemini 3.5 Flash, 87% less. Roughly tied. Gemini 3.5 Flash scores 154.7 and GPT-5.6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
Prices verified September 14, 2026.
Which should you choose?
Roughly tied. Gemini 3.5 Flash scores 154.7 and GPT-5.6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
GPT-5.6 Luna scores 67.2% on DeepSWE vs 37.4% for Gemini 3.5 Flash.
GPT-5.6 Luna scores 82.1% on FrontierMath (Tiers 1–3) vs 62.8% for Gemini 3.5 Flash.
GPT-5.6 Luna costs $0.45 per 1M tokens (3:1 input-to-output mix) vs $3.375 for Gemini 3.5 Flash, 87% less.
GPT-5.6 Luna delivers equal or higher overall capability for 87% less.
Pricing and specs
| Gemini 3.5 Flash | GPT-5.6 Luna | |
|---|---|---|
| Provider | OpenAI | |
| API model ID | gemini-3.5-flash | gpt-5.6-luna |
| Input / 1M tokens | $1.50 | $0.20 |
| Cached input / 1M tokens | $0.15 | $0.02 |
| Output / 1M tokens | $9.00 | $1.20 |
| Long-context rates | — | $0.40 in / $1.80 out on long-context requests |
| Context window | 1.05M tokens | 1.05M tokens |
| Max output | 66K tokens | 128K tokens |
| Batch discount | 50% off | 50% off |
Benchmarks
| Gemini 3.5 Flash | GPT-5.6 Luna | |
|---|---|---|
| Epoch Capabilities Index | 154.7 | 156.3 |
| GPQA Diamond· Science reasoning | 90.4% | 88.8% |
| FrontierMath (Tiers 1–3)· Advanced math | 62.8% | 82.1% |
| SimpleQA Verified· Factual accuracy | 66.2% | 41.0% |
| ARC-AGI-2· Abstract reasoning | 72.1% | 59.5% |
| DeepSWE· Coding | 37.4% | 67.2% |
| APEX-Agents· Agentic work | — | — |
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 | Gemini 3.5 Flash | GPT-5.6 Luna | Difference |
|---|---|---|---|
Support chatbot 100,000 replies a month, ~1,500 input tokens (system prompt + history) and ~400 output tokens each. | $585.00 | $78.00 | GPT-5.6 Luna 87% cheaper |
Document Q&A (RAG) 50,000 questions a month with ~8,000 tokens of retrieved context and ~600 output tokens each. | $870.00 | $116.00 | GPT-5.6 Luna 87% 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. | $402.00 | $53.60 | GPT-5.6 Luna 87% 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.
Gemini 3.5 Flash vs GPT-5.6 Luna cost calculator
- $116.00/mo$0.0023 / request
- Gemini 3.5 FlashGoogle$870.00/mo$0.02 / request
Standard-tier list prices. Long-context rates apply automatically where the provider publishes a threshold. Excludes cache-write surcharges, taxes, batch and volume discounts.
Gemini 3.5 Flash pricing notes
Google’s Gemini 3.5 Flash model, with thinking, tool use and a 1M-token context window.
- Output price includes thinking tokens.
- Context cache storage costs $1.00 per 1M tokens per hour.
- Priority inference costs 1.8x the standard rate.
GPT-5.6 Luna pricing notes
The GPT-5.6 model optimized for cost-sensitive, high-volume workloads.
- Cache writes are billed at $0.25 per 1M tokens.
- Fast mode costs 2x the standard rate; Flex costs half.
Frequently asked questions
- Is Gemini 3.5 Flash cheaper than GPT-5.6 Luna?
- GPT-5.6 Luna is 87% cheaper on input tokens ($0.20 vs $1.50 per 1M). GPT-5.6 Luna is 87% cheaper on output tokens ($1.20 vs $9.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-5.6 Luna costs $116.00 a month versus $870.00 for Gemini 3.5 Flash, 87% less.
- Which is more capable, Gemini 3.5 Flash or GPT-5.6 Luna?
- Roughly tied. Gemini 3.5 Flash scores 154.7 and GPT-5.6 Luna scores 156.3 on the Epoch Capabilities Index, and their confidence intervals overlap.
- How much does Gemini 3.5 Flash cost per 1M tokens?
- Gemini 3.5 Flash costs $1.50 per 1M input tokens and $9.00 per 1M output tokens, and $0.15 per 1M cached input tokens on Google’s standard tier.
- How much does GPT-5.6 Luna cost per 1M tokens?
- GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens, and $0.02 per 1M cached input tokens on OpenAI’s standard tier.
- Which has the larger context window, Gemini 3.5 Flash or GPT-5.6 Luna?
- GPT-5.6 Luna has the larger context window: 1.05M tokens versus 1.05M for Gemini 3.5 Flash.