Model Comparison

Seed 2.1 Pro vs GPT-5.5Which is better in 2026?

Both models are evenly matched across the benchmarks.

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

Seed 2.1 Pro (by ByteDance) and GPT-5.5 (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.

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

Choose Seed 2.1 Pro if…

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

Choose GPT-5.5 if…

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

Performance Benchmarks

Comparative analysis across standard metrics

8 benchmarks

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

Both models are evenly matched across the benchmarks.

Fri Jul 17 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).

ByteDance
Seed 2.1 Pro
Input- tokens
Output- tokens
OpenAI
GPT-5.5
Input1,050,000 tokens
Output128,000 tokens
Fri Jul 17 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

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

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

Seed 2.1 Pro

Text
Images
Audio
Video

GPT-5.5

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.

Seed 2.1 Pro

Proprietary

Closed source

GPT-5.5

Proprietary

Closed source

Release Timeline

When each model was launched

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

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

Seed 2.1 Pro

Jun 24, 2026

3 weeks ago

2mo newer
GPT-5.5

Apr 23, 2026

2 months ago

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.

Seed 2.1 Pro

—

GPT-5.5

Dec 2025

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

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%)
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%)

Detailed Comparison

Interactive Arena

Judge for yourself.

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

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

FAQ

Common questions about Seed 2.1 Pro vs GPT-5.5.

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

Both models are evenly matched across the benchmarks. Seed 2.1 Pro is made by ByteDance and GPT-5.5 is made by OpenAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does Seed 2.1 Pro compare to GPT-5.5 in benchmarks?

Seed 2.1 Pro scores CharXiv-D: 95.5%, MathVision: 94.5%, MathVista: 90.7%, MathVerse: 89.7%, Video-MME: 89.2%. GPT-5.5 scores Tau2 Telecom: 98.0%, ARC-AGI: 95.0%, GPQA: 93.6%, ARC-AGI v2: 85.0%, GDPval-MM: 84.9%.

What are the context window sizes for Seed 2.1 Pro and GPT-5.5?

Seed 2.1 Pro supports an unknown number of tokens and GPT-5.5 supports 1.1M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

Who makes Seed 2.1 Pro and GPT-5.5?

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

Related comparisons