Gemini 3.5 Flash vs GPT-5.6 Luna
Detailed pricing comparison and cost analysis.
Updated September 2026
Cost Simulator
| Feature | Gemini 3.5 Flash | GPT-5.6 Luna |
|---|---|---|
| Provider | OpenAI | |
| Input Price (1M) | $1.50 | $0.20 |
| Output Price (1M) | $9.00 | $1.20 |
| Context Window | 1,000,000 | 1,000,000 |
Verdict
Gemini 3.5 Flash costs $1.50 per 1M input tokens and $9.00 per 1M output tokens. GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens. GPT-5.6 Luna is 87% cheaper on input tokens than Gemini 3.5 Flash. For output tokens, GPT-5.6 Luna is the more affordable option at $1.20/1M vs $9.00.
On context window, Gemini 3.5 Flash supports 1,000,000 tokens — meaning it can fit more conversation history, documents, or code in a single request. This matters for RAG pipelines, long document analysis, and agentic workflows where context builds up over many turns.
When to choose Gemini 3.5 Flash
- ✓ You are already integrated with Google
When to choose GPT-5.6 Luna
- ✓ You need the lowest input token cost ($ 0.20/1M)
- ✓ Your workload is output-heavy — GPT-5.6 Luna generates text cheaper
- ✓ You are already integrated with OpenAI
Use the calculator above to simulate your specific workload and find the exact break-even point. For most applications, the cheapest model is the one that minimises your total monthly bill given your input-to-output token ratio.
Frequently Asked Questions
Is Gemini 3.5 Flash cheaper than GPT-5.6 Luna? ▼
GPT-5.6 Luna is cheaper on input tokens at $0.20/1M vs $1.50/1M for Gemini 3.5 Flash — a 87% saving.
What is the context window of Gemini 3.5 Flash vs GPT-5.6 Luna? ▼
Gemini 3.5 Flash has a 1,000,000-token context window. GPT-5.6 Luna has a 1,000,000-token context window. Gemini 3.5 Flash supports the larger context, suitable for longer documents and agentic workflows.
Which model is better: Gemini 3.5 Flash or GPT-5.6 Luna? ▼
The best choice depends on your use case. For cost efficiency on input tokens, GPT-5.6 Luna is the cheaper option. For maximum context length, Gemini 3.5 Flash supports 1,000,000 tokens. Use the comparison table above to find the right fit for your workload.