Model Comparison

GPT-5.5 vs GPT-5.6 LunaWhich is better in 2026?

GPT-5.5 has a slight edge in benchmark performance. GPT-5.6 Luna is 5.0x cheaper per token.

Verdict: GPT-5.5 vs GPT-5.6 Luna — which is better?

GPT-5.5 (by OpenAI) and GPT-5.6 Luna (by OpenAI) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.

GPT-5.5 outperforms in 5 benchmarks (BrowseComp, GPQA, MMMU-Pro, MRCR v2 (8-needle), Toolathlon), while GPT-5.6 Luna is better at 4 benchmarks (FrontierMath, GDPval-AA, Graphwalks BFS >128k, SWE-Bench Pro). GPT-5.5 has a slight edge in benchmark performance.

On price, GPT-5.6 Luna is roughly 5.0x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Choose GPT-5.5 if…

  • you want the strongest raw capability — it leads on 5 of 9 shared benchmarks

Choose GPT-5.6 Luna if…

  • cost matters — it's about 5.0x cheaper per token
  • you want the most recent training data — it shipped Jul 2026

Performance Benchmarks

Comparative analysis across standard metrics

9 benchmarks

GPT-5.5 outperforms in 5 benchmarks (BrowseComp, GPQA, MMMU-Pro, MRCR v2 (8-needle), Toolathlon), while GPT-5.6 Luna is better at 4 benchmarks (FrontierMath, GDPval-AA, Graphwalks BFS >128k, SWE-Bench Pro).

GPT-5.5 has a slight edge in benchmark performance.

Wed Jul 22 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

GPT-5.6 Luna costs less

For input processing, GPT-5.5 ($5.00/1M tokens) is 5.0x more expensive than GPT-5.6 Luna ($1.00/1M tokens).

For output processing, GPT-5.5 ($30.00/1M tokens) is 5.0x more expensive than GPT-5.6 Luna ($6.00/1M tokens).

In conclusion, GPT-5.5 is more expensive than GPT-5.6 Luna.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Wed Jul 22 2026 • llm-stats.com
OpenAI
GPT-5.5
Input tokens$5.00
Output tokens$30.00
Best providerOpenAI
OpenAI
GPT-5.6 Luna
Input tokens$1.00
Output tokens$6.00
Best providerOpenAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Both models have the same input context window of 1,050,000 tokens. Both models can generate responses up to 128,000 tokens.

OpenAI
GPT-5.5
Input1,050,000 tokens
Output128,000 tokens
OpenAI
GPT-5.6 Luna
Input1,050,000 tokens
Output128,000 tokens
Wed Jul 22 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both GPT-5.5 and GPT-5.6 Luna support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

GPT-5.5

Text
Images
Audio
Video

GPT-5.6 Luna

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-5.5

Proprietary

Closed source

GPT-5.6 Luna

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.5 was released on 2026-04-23, while GPT-5.6 Luna was released on 2026-07-09.

GPT-5.6 Luna is 3 months newer than GPT-5.5.

GPT-5.5

Apr 23, 2026

2 months ago

GPT-5.6 Luna

Jul 9, 2026

1 weeks ago

2mo newer

Knowledge Cutoff

When training data ends

GPT-5.5 has a knowledge cutoff of 2025-12-01, while GPT-5.6 Luna has a cutoff of 2026-02-16.

GPT-5.6 Luna has more recent training data (up to 2026-02-16), making it potentially better informed about events through that date compared to GPT-5.5 (2025-12-01).

GPT-5.5

Dec 2025

GPT-5.6 Luna

Feb 2026

2 mo newer

Provider Availability

GPT-5.5 is available from OpenAI. GPT-5.6 Luna is available from OpenAI.

GPT-5.5

openai logo
OpenAI
Input Price:Input: $5.00/1MOutput Price:Output: $30.00/1M

GPT-5.6 Luna

openai logo
OpenAI
Input Price:Input: $1.00/1MOutput Price:Output: $6.00/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

OpenAI
Higher BrowseComp score (84.4% vs 83.3%)
Higher GPQA score (93.6% vs 92.3%)
Higher MMMU-Pro score (83.2% vs 78.4%)
Higher MRCR v2 (8-needle) score (74.0% vs 41.3%)
Higher Toolathlon score (55.6% vs 53.4%)
OpenAI
Less expensive input tokens
Less expensive output tokens
Higher FrontierMath score (78.6% vs 35.4%)
Higher GDPval-AA score (53.1% vs 37.8%)
Higher Graphwalks BFS >128k score (81.3% vs 45.4%)
Higher SWE-Bench Pro score (62.7% vs 58.6%)

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against GPT-5.5 and GPT-5.6 Luna side-by-side, then vote on the output you prefer.

GPT-5.5
✓ Preferred
GPT-5.6 Luna
Open in Playground
AI Model Comparison Table
Feature
OpenAI
GPT-5.5
OpenAI
GPT-5.6 Luna

FAQ

Common questions about GPT-5.5 vs GPT-5.6 Luna.

Which is better, GPT-5.5 or GPT-5.6 Luna?

GPT-5.5 has a slight edge in benchmark performance. GPT-5.5 is made by OpenAI and GPT-5.6 Luna is made by OpenAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5.5 compare to GPT-5.6 Luna in benchmarks?

GPT-5.5 scores Tau2 Telecom: 98.0%, ARC-AGI: 95.0%, GPQA: 93.6%, ARC-AGI v2: 85.0%, GDPval-MM: 84.9%. GPT-5.6 Luna scores Connectors: 99.9%, HealthBench Consensus: 95.1%, GPQA: 92.3%, Search and Function-Calling: 89.7%, Capture-the-Flag Challenges (Internal): 85.2%.

Is GPT-5.5 cheaper than GPT-5.6 Luna?

GPT-5.6 Luna is 5.0x cheaper for input tokens. GPT-5.5 costs $5.00/M input and $30.00/M output via openai. GPT-5.6 Luna costs $1.00/M input and $6.00/M output via openai.

What are the context window sizes for GPT-5.5 and GPT-5.6 Luna?

GPT-5.5 supports 1.1M tokens and GPT-5.6 Luna supports 1.1M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5.5 and GPT-5.6 Luna?

Key differences include input pricing ($5.00 vs $1.00/M). See the full comparison above for benchmark-by-benchmark results.

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