Model Comparison

Gemini 3.5 Flash vs GPT-5.6 LunaWhich is better in 2026?

GPT-5.6 Luna has a slight edge in benchmark performance. GPT-5.6 Luna is 1.5x cheaper per token.

Verdict: Gemini 3.5 Flash vs GPT-5.6 Luna — which is better?

Gemini 3.5 Flash (by Google) 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.

Gemini 3.5 Flash outperforms in 2 benchmarks (MMMU-Pro, Toolathlon), while GPT-5.6 Luna is better at 3 benchmarks (GDPval-AA, MRCR v2 (8-needle), SWE-Bench Pro). GPT-5.6 Luna has a slight edge in benchmark performance.

On price, GPT-5.6 Luna is roughly 1.5x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

GPT-5.6 Luna also accepts a larger context window (1,050,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose Gemini 3.5 Flash if…

  • you want predictable pricing at $1.50/M input and $9.00/M output

Choose GPT-5.6 Luna if…

  • you want the strongest raw capability — it leads on 3 of 5 shared benchmarks
  • cost matters — it's about 1.5x cheaper per token
  • you process long inputs — it offers a 1,050,000 token context window
  • you want the most recent training data — it shipped Jul 2026

Performance Benchmarks

Comparative analysis across standard metrics

5 benchmarks

Gemini 3.5 Flash outperforms in 2 benchmarks (MMMU-Pro, Toolathlon), while GPT-5.6 Luna is better at 3 benchmarks (GDPval-AA, MRCR v2 (8-needle), SWE-Bench Pro).

GPT-5.6 Luna has a slight edge in benchmark performance.

Fri Jul 17 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, Gemini 3.5 Flash ($1.50/1M tokens) is 1.5x more expensive than GPT-5.6 Luna ($1.00/1M tokens).

For output processing, Gemini 3.5 Flash ($9.00/1M tokens) is 1.5x more expensive than GPT-5.6 Luna ($6.00/1M tokens).

In conclusion, Gemini 3.5 Flash is more expensive than GPT-5.6 Luna.*

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

Lowest available price from all providers
Fri Jul 17 2026 • llm-stats.com
Google
Gemini 3.5 Flash
Input tokens$1.50
Output tokens$9.00
Best providerGoogle
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

GPT-5.6 Luna accepts 1,050,000 input tokens compared to Gemini 3.5 Flash's 1,048,576 tokens. GPT-5.6 Luna can generate longer responses up to 128,000 tokens, while Gemini 3.5 Flash is limited to 65,536 tokens.

Google
Gemini 3.5 Flash
Input1,048,576 tokens
Output65,536 tokens
OpenAI
GPT-5.6 Luna
Input1,050,000 tokens
Output128,000 tokens
Fri Jul 17 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Gemini 3.5 Flash and GPT-5.6 Luna support multimodal inputs.

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

Gemini 3.5 Flash

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.

Gemini 3.5 Flash

Proprietary

Closed source

GPT-5.6 Luna

Proprietary

Closed source

Release Timeline

When each model was launched

Gemini 3.5 Flash was released on 2026-05-19, while GPT-5.6 Luna was released on 2026-07-09.

GPT-5.6 Luna is 2 months newer than Gemini 3.5 Flash.

Gemini 3.5 Flash

May 19, 2026

1 months ago

GPT-5.6 Luna

Jul 9, 2026

1 weeks ago

1mo newer

Knowledge Cutoff

When training data ends

Gemini 3.5 Flash has a knowledge cutoff of 2026-01-31, 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 Gemini 3.5 Flash (2026-01-31).

Gemini 3.5 Flash

Jan 2026

GPT-5.6 Luna

Feb 2026

1 mo newer

Provider Availability

Gemini 3.5 Flash is available from Google. GPT-5.6 Luna is available from OpenAI.

Gemini 3.5 Flash

google logo
Google
Input Price:Input: $1.50/1MOutput Price:Output: $9.00/1M

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

Google
Higher MMMU-Pro score (83.6% vs 78.4%)
Higher Toolathlon score (56.5% vs 53.4%)
OpenAI
Larger context window (1,050,000 tokens)
Less expensive input tokens
Less expensive output tokens
Higher GDPval-AA score (53.1% vs 45.7%)
Higher MRCR v2 (8-needle) score (41.3% vs 26.6%)
Higher SWE-Bench Pro score (62.7% vs 55.1%)

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against Gemini 3.5 Flash and GPT-5.6 Luna side-by-side, then vote on the output you prefer.

Gemini 3.5 Flash
✓ Preferred
GPT-5.6 Luna
Open in Playground
AI Model Comparison Table
Feature
Google
Gemini 3.5 Flash
OpenAI
GPT-5.6 Luna

FAQ

Common questions about Gemini 3.5 Flash vs GPT-5.6 Luna.

Which is better, Gemini 3.5 Flash or GPT-5.6 Luna?

GPT-5.6 Luna has a slight edge in benchmark performance. Gemini 3.5 Flash is made by Google 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 Gemini 3.5 Flash compare to GPT-5.6 Luna in benchmarks?

Gemini 3.5 Flash scores CharXiv-R: 84.2%, MCP Atlas: 83.6%, MMMU-Pro: 83.6%, OSWorld-Verified: 78.4%, Terminal-Bench 2.0: 76.2%. 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 Gemini 3.5 Flash cheaper than GPT-5.6 Luna?

GPT-5.6 Luna is 1.5x cheaper for input tokens. Gemini 3.5 Flash costs $1.50/M input and $9.00/M output via google. GPT-5.6 Luna costs $1.00/M input and $6.00/M output via openai.

What are the context window sizes for Gemini 3.5 Flash and GPT-5.6 Luna?

Gemini 3.5 Flash supports 1.0M 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 Gemini 3.5 Flash and GPT-5.6 Luna?

Key differences include context window (1.0M vs 1.1M), input pricing ($1.50 vs $1.00/M). See the full comparison above for benchmark-by-benchmark results.

Who makes Gemini 3.5 Flash and GPT-5.6 Luna?

Gemini 3.5 Flash is developed by Google and GPT-5.6 Luna is developed by OpenAI.

Related comparisons