Model Comparison

GPT-5.6 Luna vs Step-3.5-FlashWhich is better in 2026?

GPT-5.6 Luna significantly outperforms across most benchmarks. Step-3.5-Flash is 12.9x cheaper per token.

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

GPT-5.6 Luna (by OpenAI) and Step-3.5-Flash (by StepFun) 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-5.6 Luna outperforms in 1 benchmarks (BrowseComp), while Step-3.5-Flash is better at 0 benchmarks. GPT-5.6 Luna significantly outperforms across most benchmarks.

On price, Step-3.5-Flash is roughly 12.9x 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 GPT-5.6 Luna if…

  • you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
  • you process long inputs — it offers a 1,050,000 token context window
  • you want the most recent training data — it shipped Jul 2026

Choose Step-3.5-Flash if…

  • cost matters — it's about 12.9x cheaper per token
  • you need open weights you can self-host or fine-tune

Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

GPT-5.6 Luna outperforms in 1 benchmarks (BrowseComp), while Step-3.5-Flash is better at 0 benchmarks.

GPT-5.6 Luna significantly outperforms across most benchmarks.

Tue Jul 21 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Step-3.5-Flash costs less

For input processing, GPT-5.6 Luna ($1.00/1M tokens) is 10.0x more expensive than Step-3.5-Flash ($0.10/1M tokens).

For output processing, GPT-5.6 Luna ($6.00/1M tokens) is 15.0x more expensive than Step-3.5-Flash ($0.40/1M tokens).

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

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

Lowest available price from all providers
Tue Jul 21 2026 • llm-stats.com
OpenAI
GPT-5.6 Luna
Input tokens$1.00
Output tokens$6.00
Best providerOpenAI
StepFun
Step-3.5-Flash
Input tokens$0.10
Output tokens$0.40
Best providerStepFun
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 Step-3.5-Flash's 65,536 tokens. GPT-5.6 Luna can generate longer responses up to 128,000 tokens, while Step-3.5-Flash is limited to 8,192 tokens.

OpenAI
GPT-5.6 Luna
Input1,050,000 tokens
Output128,000 tokens
StepFun
Step-3.5-Flash
Input65,536 tokens
Output8,192 tokens
Tue Jul 21 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

GPT-5.6 Luna supports multimodal inputs, whereas Step-3.5-Flash does not.

GPT-5.6 Luna can handle both text and other forms of data like images, making it suitable for multimodal applications.

GPT-5.6 Luna

Text
Images
Audio
Video

Step-3.5-Flash

Text
Images
Audio
Video

License

Usage and distribution terms

GPT-5.6 Luna is licensed under a proprietary license, while Step-3.5-Flash uses Apache 2.0.

License differences may affect how you can use these models in commercial or open-source projects.

GPT-5.6 Luna

Proprietary

Closed source

Step-3.5-Flash

Apache 2.0

Open weights

Release Timeline

When each model was launched

GPT-5.6 Luna was released on 2026-07-09, while Step-3.5-Flash was released on 2026-02-02.

GPT-5.6 Luna is 5 months newer than Step-3.5-Flash.

GPT-5.6 Luna

Jul 9, 2026

1 weeks ago

5mo newer
Step-3.5-Flash

Feb 2, 2026

5 months ago

Knowledge Cutoff

When training data ends

GPT-5.6 Luna has a documented knowledge cutoff of 2026-02-16, while Step-3.5-Flash's cutoff date is not specified.

We can confirm GPT-5.6 Luna's training data extends to 2026-02-16, but cannot make a direct comparison without Step-3.5-Flash's cutoff date.

GPT-5.6 Luna

Feb 2026

Step-3.5-Flash

—

Provider Availability

GPT-5.6 Luna is available from OpenAI. Step-3.5-Flash is available from StepFun.

GPT-5.6 Luna

openai logo
OpenAI
Input Price:Input: $1.00/1MOutput Price:Output: $6.00/1M

Step-3.5-Flash

stepfun logo
StepFun
Input Price:Input: $0.10/1MOutput Price:Output: $0.40/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

OpenAI
Larger context window (1,050,000 tokens)
Supports multimodal inputs
Higher BrowseComp score (83.3% vs 69.0%)
StepFun
Less expensive input tokens
Less expensive output tokens
Has open weights

Detailed Comparison

Interactive Arena

Judge for yourself.

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

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

FAQ

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

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

GPT-5.6 Luna significantly outperforms across most benchmarks. GPT-5.6 Luna is made by OpenAI and Step-3.5-Flash is made by StepFun. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5.6 Luna compare to Step-3.5-Flash in benchmarks?

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%. Step-3.5-Flash scores AIME 2025: 97.3%, Tau-bench: 88.2%, LiveCodeBench v6: 86.4%, IMO-AnswerBench: 85.4%, SWE-Bench Verified: 74.4%.

Is GPT-5.6 Luna cheaper than Step-3.5-Flash?

Step-3.5-Flash is 10.0x cheaper for input tokens. GPT-5.6 Luna costs $1.00/M input and $6.00/M output via openai. Step-3.5-Flash costs $0.10/M input and $0.40/M output via stepfun.

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

GPT-5.6 Luna supports 1.1M tokens and Step-3.5-Flash supports 66K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5.6 Luna and Step-3.5-Flash?

Key differences include context window (1.1M vs 66K), input pricing ($1.00 vs $0.10/M), multimodal support (yes vs no), licensing (Proprietary vs Apache 2.0). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5.6 Luna and Step-3.5-Flash?

GPT-5.6 Luna is developed by OpenAI and Step-3.5-Flash is developed by StepFun.

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