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GPT-5.6 Luna vs Seed 2.1 Pro

GPT-5.6 Luna and Seed 2.1 Pro are closely matched at 45.4 and 46.4 on the LLM Stats Score.

OpenAI · ByteDance · Updated for 2026

Which is better?

GPT-5.6 Luna and Seed 2.1 Pro are closely matched on the overall LLM Stats Score at 45.4 and 46.4.

In the 7 individual benchmarks reported for both models, GPT-5.6 Luna wins 5; this is a narrower head-to-head signal than the composite indexes.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose GPT-5.6 Luna

  • you value its reported benchmark strengths — it wins 5 of 7 exact shared results
  • you want the most recent training data — it shipped Jul 2026

Choose Seed 2.1 Pro

  • you are already invested in the ByteDance ecosystem

At a glance

The differences that matter most.

GPT-5.6 Luna
OpenAI
Seed 2.1 Pro
ByteDance
Core performance indexes
LLM Stats Score
45.4
#29
46.4
#25
Reasoning
44.4
#33
47.2
#22
Coding
36.5
#19
33.7
#31
Agents
31.3
#25
31.3
#26
Cost, coverage & limits
Benchmark wins
5 of 7
2 of 7
Input price
$0.20 / M
— / M
Output price
$1.20 / M
— / M
Context window
1,050,000
—

Capability indexes

Additional strengths measured across groups of related public benchmarks

6 shared
Index
GPT-5.6 Luna
Seed 2.1 Pro
Math
28.7#86
39.1#20
Vision
24.7#49
34.2#12
Tool use
25.6#32
26.4#27
Long context
21.3#23
28.8#5
Multimodal
25.5#43
37.4#4
1 more shared indexes
Finance
-1.5#195
34.0#7
Conservative TrueSkill rating · higher is betterHow scores work

Individual benchmarks

45 reported for GPT-5.6 Luna · 94 for Seed 2.1 Pro

7 shared

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.

Sat Sep 05 2026 • llm-stats.com

Human preference

Blind head-to-head votes and playground preference scores

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
Sat Sep 05 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

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

1 months ago

2w newer
Seed 2.1 Pro

Jun 24, 2026

2 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

—

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

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

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 and Seed 2.1 Pro are closely matched on the LLM Stats Score at 45.4 and 46.4. 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 capability indexes, individual benchmarks, pricing, and limits 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.

What are the main differences between GPT-5.6 Luna and Seed 2.1 Pro?

Key differences include LLM Stats Score (45.4 vs 46.4). See the full comparison above for benchmark-by-benchmark results.

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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