AI model comparison
GPT-6 Luna vs Gemini 3.8 Flash
Pricing, context window, benchmarks, and features compared side by side. Or skip the guesswork and send one prompt to both.
OpenAI
GPT-6 Luna
GPT-6 Luna is the fast, cost-efficient model in OpenAI's GPT-6 series, positioned below GPT-6 Sol.
- Input / 1M
- $0.10
- Output / 1M
- $0.50
- Context
- 1.05M
Gemini 3.8 Flash
Gemini 3.8 Flash is Google's most intelligent Flash model with significant gains from 3.7 Flash across software engineering, agentic tasks, and multi-step reasoning.
- Input / 1M
- $0.75
- Output / 1M
- $3.75
- Context
- 1.05M
At a glance
Quick verdict
How the two models stack up on the things people ask about most.
Lower price
GPT-6 Luna
7.5x cheaper for a typical chat
Higher intelligence score
Gemini 3.8 Flash
40.9 vs 38.1 on Artificial Analysis
Larger context window
GPT-6 Luna
1.05M vs 1.05M tokens
Newer release
GPT-6 Luna
Released September 22, 2026
Benchmarks
Benchmark scores
Independent scores from Artificial Analysis. Higher is better.
Intelligence index
GPT-6 Luna38.1Gemini 3.8 Flash40.9Coding index
GPT-6 LunaNot availableGemini 3.8 Flash76.3Agentic index
GPT-6 LunaNot availableGemini 3.8 Flash40.2Pricing
GPT-6 Luna vs Gemini 3.8 Flash API pricing
Per-token API rates. Cheaper option highlighted.
| Metric | GPT-6 Luna | Gemini 3.8 Flash |
|---|---|---|
| Input tokensPer 1M tokens | $0.10 | $0.75 |
| Output tokensPer 1M tokens | $0.50 | $3.75 |
| Cached input (read)Per 1M tokens | $0.01 | $0.08 |
| Cache writePer 1M tokens | $0.13 | $0.04 |
| Long-context pricingPer 1M tokens, for very long prompts | $0.20 in / $0.75 out above 272K | Same rate at any length |
| Web searchPer request | $0.01 | $0.014 |
What it costs in practice
Estimated cost per 1,000 requests at standard rates. Coding and long-document figures also show the cost when the input is already cached.
Chat message
2K in, 500 out
GPT-6 Luna$0.45Gemini 3.8 Flash$3.38Coding task
30K in, 4K out
GPT-6 Luna$5$2.30 cachedGemini 3.8 Flash$37.50$17.25 cachedLong document summary
150K in, 2K out
GPT-6 Luna$16$2.50 cachedGemini 3.8 Flash$120$18.75 cachedSpecs
Context window and capabilities
How much each model can read, how much it can write, and what it accepts as input.
| Metric | GPT-6 Luna | Gemini 3.8 Flash |
|---|---|---|
| Context window | 1.05M tokens | 1.05M tokens |
| Max output | 128K tokens | 66K tokens |
| Input types | File, Image, Text | Audio, File, Image, Text, Video |
| Output types | Text | Text |
| Reasoning effort levels | Max, Extra high, High, Medium, Low, None | High, Medium, Low |
| Default reasoning effort | Medium | Medium |
| Release date | September 22, 2026 | September 2, 2026 |
Features
Supported features
API features available for each model.
| Metric | GPT-6 Luna | Gemini 3.8 Flash |
|---|---|---|
| Tool calling | Supported | Supported |
| Structured outputs | Supported | Supported |
| JSON mode | Supported | Supported |
| Reasoning | Supported | Supported |
| Temperature | Not supported | Supported |
| Stop sequences | Not supported | Supported |
| Deterministic seed | Supported | Supported |
| Verbosity control | Supported | Not supported |
Keep exploring
More on these models
Other head-to-heads, the full model page, and the alternatives list for each model.
GPT-6 LunaView full model details- GPT-6 Luna vs DeepSeek V4.1 Flash
- GPT-6 Luna vs GLM 5.3 Flash
- GPT-6 Luna vs MiMo-V2.6-Flash
- GPT-6 Luna vs Hy4 preview
- GPT-6 Luna vs DeepSeek V4 Flash 0731
- GPT-6 Luna vs Claude Opus 5.5
- GPT-6 Luna vs GLM 5.3
- GPT-6 Luna vs DeepSeek V4 Flash 0423
- GPT-6 Luna vs Step 5 Preview
- GPT-6 Luna vs Hy3
- GPT-6 Luna vs GPT-5.6 Luna
- GPT-6 Luna vs GPT-6.1 Sol
- GPT-6 Luna vs Muse Spark 1.3 Contributor
- GPT-6 Luna vs Claude Sonnet 5.5
- GPT-6 Luna vs MiMo-V2.6-Pro
- GPT-6 Luna vs DeepSeek V4 Pro 0813
- GPT-6 Luna vs GPT-6 Astra
- GPT-6 Luna vs Claude Opus 5
- GPT-6 Luna vs Claude Fable 5.1
- GPT-6 Luna vs DeepSeek V4 Pro 0423
- GPT-6 Luna vs Solar Pro 4
- GPT-6 Luna vs GPT-6 Luna Pro
- GPT-6 Luna vs Claude Haiku 5.5
- GPT-6 Luna vs Ling 3.1 Flash
- GPT-6 Luna vs Qwen3.8 Flash
- GPT-6 Luna vs Qwen3.7 Flash
- GPT-6 Luna vs DeepSeek V4 Flash Vision Exp
- GPT-6 Luna vs GLM 5.3 FlashX
- GPT-6 Luna vs GPT-5.6 Luna Pro
Gemini 3.8 FlashView full model details- Gemini 3.8 Flash vs DeepSeek V4.1 Flash
- Gemini 3.8 Flash vs GLM 5.3 Flash
- Gemini 3.8 Flash vs MiMo-V2.6-Flash
- Gemini 3.8 Flash vs Hy4 preview
- Gemini 3.8 Flash vs DeepSeek V4 Flash 0731
- Gemini 3.8 Flash vs Claude Opus 5.5
- Gemini 3.8 Flash vs GLM 5.3
- Gemini 3.8 Flash vs DeepSeek V4 Flash 0423
- Gemini 3.8 Flash vs Step 5 Preview
- Gemini 3.8 Flash vs Hy3
- Gemini 3.8 Flash vs GPT-5.6 Luna
- Gemini 3.8 Flash vs GPT-6 Astra
- Gemini 3.8 Flash vs Kimi K3
- Gemini 3.8 Flash vs Muse Spark 1.3
- Gemini 3.8 Flash vs Grok 4.7
- Gemini 3.8 Flash vs DeepSeek V4 Pro 0813
- Gemini 3.8 Flash vs Qwen3.8 Max (0902)
- Gemini 3.8 Flash vs Grok 4.6
- Gemini 3.8 Flash vs Claude Haiku 5.5
- Gemini 3.8 Flash vs GPT-5.6 Terra
- Gemini 3.8 Flash vs Claude Sonnet 5
- Gemini 3.8 Flash vs Claude Opus 4.8
- Gemini 3.8 Flash vs Ling 3.1 Flash
- Gemini 3.8 Flash vs Claude Opus 4.7
- Gemini 3.8 Flash vs Qwen3.8 2.4T A95B
- Gemini 3.8 Flash vs Gemini 3.7 Flash
- Gemini 3.8 Flash vs Muse Spark 1.2
- Gemini 3.8 Flash vs GPT-5.4
- Gemini 3.8 Flash vs Grok 4.5
- Gemini 3.8 Flash vs GPT-5.5
- Gemini 3.8 Flash vs Gemini 3.6 Flash
- Gemini 3.8 Flash vs Muse Spark 1.1
- Gemini 3.8 Flash vs Gemini 3.5 Flash
Our take
Gemini 3.8 Flash is the stronger cheap model: higher intelligence (40.9 vs 37.3) and usually the better default for everyday work. Luna is the OpenAI-shaped alternative if you want that family's style at flash-tier pricing.
FAQ
Frequently asked questions
Is GPT-6 Luna or Gemini 3.8 Flash cheaper?
GPT-6 Luna is cheaper for a typical chat (2K input tokens and 500 output tokens). GPT-6 Luna costs $0.10 per 1M input tokens and $0.50 per 1M output tokens, while Gemini 3.8 Flash costs $0.75 per 1M input tokens and $3.75 per 1M output tokens.
Which has a bigger context window, GPT-6 Luna or Gemini 3.8 Flash?
GPT-6 Luna supports up to 1.05M tokens of context, compared with 1.05M for Gemini 3.8 Flash.
Is GPT-6 Luna smarter than Gemini 3.8 Flash?
On the Artificial Analysis Intelligence Index, GPT-6 Luna scores 38.1 and Gemini 3.8 Flash scores 40.9, putting Gemini 3.8 Flash ahead. Benchmarks don't capture everything, so the best test is running your own prompts through both.
Can I use GPT-6 Luna and Gemini 3.8 Flash at the same time?
Yes. Shortcut Chat sends one prompt to multiple models at once, so you can see GPT-6 Luna and Gemini 3.8 Flash answer side by side and keep the better response.
Why choose? Ask both.
Send one prompt to GPT-6 Luna and Gemini 3.8 Flash at the same time. Compare the answers side by side and keep the best one.