The AI arena is free today

Open Superagent

Claude Opus 5.5 vs Seed 2.1 Pro

Claude Opus 5.5 leads the LLM Stats Score 60.4 to 45.8.

Anthropic · ByteDance · Updated for 2026

Which is better?

Claude Opus 5.5 leads the overall LLM Stats Score 60.4 to 45.8, ranking #1 overall.

In the 3 individual benchmarks reported for both models, Claude Opus 5.5 wins 2; 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 Claude Opus 5.5

  • overall performance matters — it scores 60.4 and ranks #1 on LLM Stats
  • your work emphasizes reasoning and coding — it leads those capability indexes
  • you value its reported benchmark strengths — it wins 2 of 3 exact shared results
  • you want the most recent training data — it shipped Sep 2026

Choose Seed 2.1 Pro

  • you are already invested in the ByteDance ecosystem

At a glance

The differences that matter most.

Claude Opus 5.5
Anthropic
Seed 2.1 Pro
ByteDance
Core performance indexes
LLM Stats Score
60.4
#1
45.8
#35
Reasoning
59.0
#1
47.1
#29
Coding
51.0
#1
32.0
#48
Agents
45.3
#1
30.9
#36
Cost, coverage & limits
Benchmark wins
2 of 3
1 of 3
Input price
$4.00 / M
— / M
Output price
$20.00 / M
— / M
Context window
1,000,000
—

Capability indexes

Additional strengths measured across groups of related public benchmarks

4 shared
Index
Claude Opus 5.5
Seed 2.1 Pro
Math
41.8#6
40.0#15
Vision
41.3#1
34.3#16
Tool use
32.8#3
24.2#39
Multimodal
40.9#1
37.5#6
Conservative TrueSkill rating · higher is betterHow scores work

Individual benchmarks

31 reported for Claude Opus 5.5 · 94 for Seed 2.1 Pro

3 shared

Claude Opus 5.5 outperforms in 2 benchmarks (Program Bench, SWE-Bench Pro), while Seed 2.1 Pro is better at 1 benchmark (OfficeQA Pro).

Claude Opus 5.5 shows notably better performance in the majority of benchmarks.

Fri Oct 09 2026 • llm-stats.com

Human preference

Blind head-to-head votes and playground preference scores

Context Window

Maximum input and output token capacity

Only Claude Opus 5.5 specifies input context (1,000,000 tokens). Only Claude Opus 5.5 specifies output context (128,000 tokens).

Anthropic
Claude Opus 5.5
Input1,000,000 tokens
Output128,000 tokens
ByteDance
Seed 2.1 Pro
Input- tokens
Output- tokens
Fri Oct 09 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both Claude Opus 5.5 and Seed 2.1 Pro support multimodal inputs.

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

Claude Opus 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.

Claude Opus 5.5

Proprietary

Closed source

Seed 2.1 Pro

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Opus 5.5 was released on 2026-09-22, while Seed 2.1 Pro was released on 2026-06-24.

Claude Opus 5.5 is 3 months newer than Seed 2.1 Pro.

Claude Opus 5.5

Sep 22, 2026

2 weeks ago

3mo newer
Seed 2.1 Pro

Jun 24, 2026

3 months ago

Knowledge Cutoff

When training data ends

Claude Opus 5.5 has a documented knowledge cutoff of 2026-06-01, while Seed 2.1 Pro's cutoff date is not specified.

We can confirm Claude Opus 5.5's training data extends to 2026-06-01, but cannot make a direct comparison without Seed 2.1 Pro's cutoff date.

Claude Opus 5.5

Jun 2026

Seed 2.1 Pro

—

Outputs Comparison

Notice missing or incorrect data?

Judge for yourself.

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

Claude Opus 5.5
✓ Preferred
Seed 2.1 Pro
Open in Playground

FAQ

Common questions about Claude Opus 5.5 vs Seed 2.1 Pro.

Which is better, Claude Opus 5.5 or Seed 2.1 Pro?

Claude Opus 5.5 leads the LLM Stats Score 60.4 to 45.8. Claude Opus 5.5 is made by Anthropic 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 Claude Opus 5.5 compare to Seed 2.1 Pro in benchmarks?

Claude Opus 5.5 scores BenchCAD (with Python tool): 96.2%, Global-MMLU: 94.3%, SWE-bench Multilingual: 93.9%, MILU: 93.1%, ArXivMath: 91.2%. 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 Claude Opus 5.5 and Seed 2.1 Pro?

Claude Opus 5.5 supports 1.0M 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 Claude Opus 5.5 and Seed 2.1 Pro?

Key differences include LLM Stats Score (60.4 vs 45.8). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Opus 5.5 and Seed 2.1 Pro?

Claude Opus 5.5 is developed by Anthropic and Seed 2.1 Pro is developed by ByteDance.

Related comparisons