Model Comparison

GPT-5.6 Luna vs Seed 2.1 ProWhich is better in 2026?

GPT-5.6 Luna shows notably better performance in the majority of benchmarks.

Verdict: GPT-5.6 Luna vs Seed 2.1 Pro — which is better?

GPT-5.6 Luna (by OpenAI) and Seed 2.1 Pro (by ByteDance) 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 5 benchmarks (Agents' Last Exam, DeepSWE, SWE-Bench Pro, Terminal-Bench 2.1, Toolathlon), while Seed 2.1 Pro is better at 2 benchmarks (BrowseComp, MMMU-Pro). GPT-5.6 Luna shows notably better performance in the majority of benchmarks.

Choose GPT-5.6 Luna if…

  • you want the strongest raw capability — it leads on 5 of 7 shared benchmarks
  • you want the most recent training data — it shipped Jul 2026

Choose Seed 2.1 Pro if…

  • you are already invested in the ByteDance ecosystem

Performance Benchmarks

Comparative analysis across standard metrics

7 benchmarks

GPT-5.6 Luna outperforms in 5 benchmarks (Agents' Last Exam, DeepSWE, SWE-Bench Pro, Terminal-Bench 2.1, Toolathlon), while Seed 2.1 Pro is better at 2 benchmarks (BrowseComp, MMMU-Pro).

GPT-5.6 Luna shows notably better performance in the majority of benchmarks.

Sun Jul 26 2026 • llm-stats.com

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only GPT-5.6 Luna specifies input context (1,050,000 tokens). Only GPT-5.6 Luna specifies output context (128,000 tokens).

OpenAI
GPT-5.6 Luna
Input1,050,000 tokens
Output128,000 tokens
ByteDance
Seed 2.1 Pro
Input- tokens
Output- tokens
Sun Jul 26 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both GPT-5.6 Luna and Seed 2.1 Pro support multimodal inputs.

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

GPT-5.6 Luna

Text
Images
Audio
Video

Seed 2.1 Pro

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-5.6 Luna

Proprietary

Closed source

Seed 2.1 Pro

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.6 Luna was released on 2026-07-09, while Seed 2.1 Pro was released on 2026-06-24.

GPT-5.6 Luna is 1 month newer than Seed 2.1 Pro.

GPT-5.6 Luna

Jul 9, 2026

2 weeks ago

2w newer
Seed 2.1 Pro

Jun 24, 2026

1 months ago

Knowledge Cutoff

When training data ends

GPT-5.6 Luna has a documented knowledge cutoff of 2026-02-16, while Seed 2.1 Pro'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 Seed 2.1 Pro's cutoff date.

GPT-5.6 Luna

Feb 2026

Seed 2.1 Pro

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Outputs Comparison

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Key Takeaways

OpenAI
Larger context window (1,050,000 tokens)
Higher Agents' Last Exam score (50.3% vs 41.4%)
Higher DeepSWE score (67.2% vs 32.7%)
Higher SWE-Bench Pro score (62.7% vs 57.5%)
Higher Terminal-Bench 2.1 score (84.7% vs 71.0%)
Higher Toolathlon score (53.4% vs 50.6%)
ByteDance
Higher BrowseComp score (86.2% vs 83.3%)
Higher MMMU-Pro score (82.7% vs 78.4%)

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against GPT-5.6 Luna and Seed 2.1 Pro side-by-side, then vote on the output you prefer.

GPT-5.6 Luna
✓ Preferred
Seed 2.1 Pro
Open in Playground
AI Model Comparison Table
Feature
OpenAI
GPT-5.6 Luna
ByteDance
Seed 2.1 Pro

FAQ

Common questions about GPT-5.6 Luna vs Seed 2.1 Pro.

Which is better, GPT-5.6 Luna or Seed 2.1 Pro?

GPT-5.6 Luna shows notably better performance in the majority of benchmarks. GPT-5.6 Luna is made by OpenAI and Seed 2.1 Pro is made by ByteDance. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5.6 Luna compare to Seed 2.1 Pro 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%. Seed 2.1 Pro scores CharXiv-D: 95.5%, MathVision: 94.5%, MathVista: 90.7%, MathVerse: 89.7%, Video-MME: 89.2%.

What are the context window sizes for GPT-5.6 Luna and Seed 2.1 Pro?

GPT-5.6 Luna supports 1.1M tokens and Seed 2.1 Pro supports an unknown number of tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

Who makes GPT-5.6 Luna and Seed 2.1 Pro?

GPT-5.6 Luna is developed by OpenAI and Seed 2.1 Pro is developed by ByteDance.

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