Model Comparison

GPT-5.5 vs Seed 2.1 ProWhich is better in 2026?

Both models are evenly matched across the benchmarks.

Verdict: GPT-5.5 vs Seed 2.1 Pro — which is better?

GPT-5.5 (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-5.5 outperforms in 4 benchmarks (CyberGym, MMMU-Pro, SWE-Bench Pro, Toolathlon), while Seed 2.1 Pro is better at 4 benchmarks (BrowseComp, Humanity's Last Exam, MCP Atlas, OfficeQA Pro). Both models are evenly matched across the benchmarks.

Choose GPT-5.5 if…

  • you want predictable pricing at $5.00/M input and $30.00/M output

Choose Seed 2.1 Pro if…

  • you want the most recent training data — it shipped Jun 2026

Performance Benchmarks

Comparative analysis across standard metrics

8 benchmarks

GPT-5.5 outperforms in 4 benchmarks (CyberGym, MMMU-Pro, SWE-Bench Pro, Toolathlon), while Seed 2.1 Pro is better at 4 benchmarks (BrowseComp, Humanity's Last Exam, MCP Atlas, OfficeQA Pro).

Both models are evenly matched across the benchmarks.

Sun Jul 26 2026 • llm-stats.com

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only GPT-5.5 specifies input context (1,050,000 tokens). Only GPT-5.5 specifies output context (128,000 tokens).

OpenAI
GPT-5.5
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-5.5 and Seed 2.1 Pro support multimodal inputs.

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

GPT-5.5

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-5.5

Proprietary

Closed source

Seed 2.1 Pro

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.5 was released on 2026-04-23, while Seed 2.1 Pro was released on 2026-06-24.

Seed 2.1 Pro is 2 months newer than GPT-5.5.

GPT-5.5

Apr 23, 2026

3 months ago

Seed 2.1 Pro

Jun 24, 2026

1 months ago

2mo newer

Knowledge Cutoff

When training data ends

GPT-5.5 has a documented knowledge cutoff of 2025-12-01, while Seed 2.1 Pro's cutoff date is not specified.

We can confirm GPT-5.5's training data extends to 2025-12-01, but cannot make a direct comparison without Seed 2.1 Pro's cutoff date.

GPT-5.5

Dec 2025

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 CyberGym score (81.8% vs 70.2%)
Higher MMMU-Pro score (83.2% vs 82.7%)
Higher SWE-Bench Pro score (58.6% vs 57.5%)
Higher Toolathlon score (55.6% vs 50.6%)
ByteDance
Higher BrowseComp score (86.2% vs 84.4%)
Higher Humanity's Last Exam score (55.7% vs 52.2%)
Higher MCP Atlas score (83.8% vs 75.3%)
Higher OfficeQA Pro score (72.2% vs 54.1%)

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against GPT-5.5 and Seed 2.1 Pro side-by-side, then vote on the output you prefer.

GPT-5.5
✓ Preferred
Seed 2.1 Pro
Open in Playground
AI Model Comparison Table
Feature
OpenAI
GPT-5.5
ByteDance
Seed 2.1 Pro

FAQ

Common questions about GPT-5.5 vs Seed 2.1 Pro.

Which is better, GPT-5.5 or Seed 2.1 Pro?

Both models are evenly matched across the benchmarks. GPT-5.5 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-5.5 compare to Seed 2.1 Pro 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%. 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-5.5 and Seed 2.1 Pro?

GPT-5.5 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-5.5 and Seed 2.1 Pro?

GPT-5.5 is developed by OpenAI and Seed 2.1 Pro is developed by ByteDance.

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