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Claude Mythos 5.1 vs Seed 2.1 Pro

Claude Mythos 5.1 and Seed 2.1 Pro are closely matched at 45.3 and 46.2 on the LLM Stats Score.

Anthropic · ByteDance · Updated for 2026

Which is better?

Claude Mythos 5.1 and Seed 2.1 Pro are closely matched on the overall LLM Stats Score at 45.3 and 46.2.

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

Choose Claude Mythos 5.1

  • your work emphasizes coding and agents — it leads those capability indexes
  • 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 Mythos 5.1
Anthropic
Seed 2.1 Pro
ByteDance
Core performance indexes
LLM Stats Score
45.3
#33
46.2
#27
Reasoning
44.1
#36
47.4
#24
Coding
38.0
#18
33.4
#37
Agents
34.9
#22
31.8
#31
Cost, coverage & limits
Benchmark wins
—
—
Input price
$10.00 / M
— / M
Output price
$50.00 / M
— / M
Context window
1,000,000
—

Individual benchmarks

1 reported for Claude Mythos 5.1 · 94 for Seed 2.1 Pro

No common benchmarks found

Claude Mythos 5.1 and Seed 2.1 Prodon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Human preference

Blind head-to-head votes and playground preference scores

Context Window

Maximum input and output token capacity

Only Claude Mythos 5.1 specifies input context (1,000,000 tokens). Only Claude Mythos 5.1 specifies output context (128,000 tokens).

Anthropic
Claude Mythos 5.1
Input1,000,000 tokens
Output128,000 tokens
ByteDance
Seed 2.1 Pro
Input- tokens
Output- tokens
Tue Sep 22 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both Claude Mythos 5.1 and Seed 2.1 Pro support multimodal inputs.

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

Claude Mythos 5.1

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 Mythos 5.1

Proprietary

Closed source

Seed 2.1 Pro

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Mythos 5.1 was released on 2026-09-01, while Seed 2.1 Pro was released on 2026-06-24.

Claude Mythos 5.1 is 2 months newer than Seed 2.1 Pro.

Claude Mythos 5.1

Sep 1, 2026

3 weeks ago

2mo newer
Seed 2.1 Pro

Jun 24, 2026

3 months ago

Knowledge Cutoff

When training data ends

Neither model specifies a knowledge cutoff date.

Unable to compare the recency of their training data.

No cutoff dates available

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against Claude Mythos 5.1 and Seed 2.1 Pro side-by-side, then vote on the output you prefer.

Claude Mythos 5.1
✓ Preferred
Seed 2.1 Pro
Open in Playground

FAQ

Common questions about Claude Mythos 5.1 vs Seed 2.1 Pro.

Which is better, Claude Mythos 5.1 or Seed 2.1 Pro?

Claude Mythos 5.1 and Seed 2.1 Pro are closely matched on the LLM Stats Score at 45.3 and 46.2. Claude Mythos 5.1 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 Mythos 5.1 compare to Seed 2.1 Pro in benchmarks?

Claude Mythos 5.1 scores Terminal-Bench 4.0: 60.9%. 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 Claude Mythos 5.1 and Seed 2.1 Pro?

Claude Mythos 5.1 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 Mythos 5.1 and Seed 2.1 Pro?

Key differences include LLM Stats Score (45.3 vs 46.2). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Mythos 5.1 and Seed 2.1 Pro?

Claude Mythos 5.1 is developed by Anthropic and Seed 2.1 Pro is developed by ByteDance.

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