AI model comparison
GPT-5.6 Luna vs GPT-5.5
Pricing, context window, benchmarks, and features compared side by side. Or skip the guesswork and send one prompt to both.
OpenAI
GPT-5.6 Luna
GPT-5.6 Luna is a fast, cost-efficient model in OpenAI's GPT-5.6 series.
- Input / 1M
- $0.20
- Output / 1M
- $1.20
- Context
- 1.05M
OpenAI
GPT-5.5
GPT-5.5 is OpenAI’s frontier model designed for complex professional workloads, building on GPT-5.4 with stronger reasoning, higher reliability, and improved token efficiency on hard tasks.
- Input / 1M
- $5
- Output / 1M
- $30
- Context
- 1.05M
At a glance
Quick verdict
How the two models stack up on the things people ask about most.
Lower price
GPT-5.6 Luna
25x cheaper for a typical chat
Higher intelligence score
GPT-5.5
38.4 vs 37.3 on Artificial Analysis
Larger context window
Tie
1.05M vs 1.05M tokens
Newer release
GPT-5.6 Luna
Released July 9, 2026
Benchmarks
Benchmark scores
Independent scores from Artificial Analysis. Higher is better.
Intelligence index
GPT-5.6 Luna37.3GPT-5.538.4Coding index
GPT-5.6 Luna71.4GPT-5.574.9Agentic index
GPT-5.6 Luna42.1GPT-5.536.4Pricing
GPT-5.6 Luna vs GPT-5.5 API pricing
Per-token API rates. Cheaper option highlighted.
| Metric | GPT-5.6 Luna | GPT-5.5 |
|---|---|---|
| Input tokensPer 1M tokens | $0.20 | $5 |
| Output tokensPer 1M tokens | $1.20 | $30 |
| Cached input (read)Per 1M tokens | $0.02 | $0.50 |
| Cache writePer 1M tokens | $0.25 | Not available |
| Long-context pricingPer 1M tokens, for very long prompts | $0.40 in / $1.80 out above 272K | $10 in / $45 out above 272K |
| Web searchPer request | $0.01 | $0.01 |
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-5.6 Luna$1GPT-5.5$25Coding task
30K in, 4K out
GPT-5.6 Luna$10.80$5.40 cachedGPT-5.5$270$135 cachedLong document summary
150K in, 2K out
GPT-5.6 Luna$32.40$5.40 cachedGPT-5.5$810$135 cachedSpecs
Context window and capabilities
How much each model can read, how much it can write, and what it accepts as input.
| Metric | GPT-5.6 Luna | GPT-5.5 |
|---|---|---|
| Context window | 1.05M tokens | 1.05M tokens |
| Max output | 128K tokens | 128K tokens |
| Input types | File, Image, Text | File, Image, Text |
| Output types | Text | Text |
| Reasoning effort levels | Max, Extra high, High, Medium, Low, None | Extra high, High, Medium, Low, None |
| Default reasoning effort | Medium | Medium |
| Release date | July 9, 2026 | April 24, 2026 |
Features
Supported features
API features available for each model.
| Metric | GPT-5.6 Luna | GPT-5.5 |
|---|---|---|
| Tool calling | Supported | Supported |
| Structured outputs | Supported | Supported |
| JSON mode | Supported | Supported |
| Reasoning | Supported | Supported |
| Temperature | Not supported | Not supported |
| Stop sequences | Not supported | Not supported |
| Deterministic seed | Supported | Supported |
| Verbosity control | Supported | Supported |
Keep exploring
More on these models
Other head-to-heads, the full model page, and the alternatives list for each model.
GPT-5.6 LunaView full model details- GPT-5.6 Luna vs DeepSeek V4.1 Flash
- GPT-5.6 Luna vs GLM 5.3 Flash
- GPT-5.6 Luna vs MiMo-V2.6-Flash
- GPT-5.6 Luna vs Hy4 preview
- GPT-5.6 Luna vs GPT-6 Luna
- GPT-5.6 Luna vs DeepSeek V4 Flash 0731
- GPT-5.6 Luna vs Gemini 3.8 Flash
- GPT-5.6 Luna vs DeepSeek V4 Pro 0813
- GPT-5.6 Luna vs Claude Haiku 5.5
- GPT-5.6 Luna vs GPT-6 Luna Pro
- GPT-5.6 Luna vs Qwen3.8 27B
- GPT-5.6 Luna vs Gemini 3.7 Flash
- GPT-5.6 Luna vs Muse Spark 1.2
- GPT-5.6 Luna vs DeepSeek V4 Flash Vision Exp
- GPT-5.6 Luna vs Muse Spark 1.1
- GPT-5.6 Luna vs GLM 5.3 FlashX
- GPT-5.6 Luna vs GPT-5.6 Luna Pro
Our take
GPT-5.6 Luna is 25x cheaper for a typical chat. GPT-5.5 scores higher on the Artificial Analysis Intelligence Index (38.4 vs 37.3). The right pick depends on your workload, so the quickest way to settle it is to send the same prompt to both and compare.
FAQ
Frequently asked questions
Is GPT-5.6 Luna or GPT-5.5 cheaper?
GPT-5.6 Luna is cheaper for a typical chat (2K input tokens and 500 output tokens). GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens, while GPT-5.5 costs $5 per 1M input tokens and $30 per 1M output tokens.
Which has a bigger context window, GPT-5.6 Luna or GPT-5.5?
GPT-5.6 Luna supports up to 1.05M tokens of context, compared with 1.05M for GPT-5.5.
Is GPT-5.6 Luna smarter than GPT-5.5?
On the Artificial Analysis Intelligence Index, GPT-5.6 Luna scores 37.3 and GPT-5.5 scores 38.4, putting GPT-5.5 ahead. Benchmarks don't capture everything, so the best test is running your own prompts through both.
Can I use GPT-5.6 Luna and GPT-5.5 at the same time?
Yes. Shortcut Chat sends one prompt to multiple models at once, so you can see GPT-5.6 Luna and GPT-5.5 answer side by side and keep the better response.
Why choose? Ask both.
Send one prompt to GPT-5.6 Luna and GPT-5.5 at the same time. Compare the answers side by side and keep the best one.