Claude Opus 5.5 vs Seed 1.8

Claude Opus 5.5 leads the LLM Stats Score 59.7 to 34.1. Seed 1.8 is 11.6x cheaper per token.

Anthropic · ByteDance · Updated for 2026

Which is better?

Claude Opus 5.5 leads the overall LLM Stats Score 59.7 to 34.1, ranking #1 overall.

In the 1 individual benchmarks reported for both models, Claude Opus 5.5 wins 1; this is a narrower head-to-head signal than the composite indexes.

On price, Seed 1.8 is roughly 11.6x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Claude Opus 5.5 also accepts a larger context window (1,000,000 input tokens), making it the stronger choice for long documents and large codebases.

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

Choose Claude Opus 5.5

overall performance matters — it scores 59.7 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 1 of 1 exact shared results
you process long inputs — it offers a 1,000,000 token context window
you want the most recent training data — it shipped Sep 2026

Choose Seed 1.8

cost matters — it's about 11.6x cheaper per token

At a glance

The differences that matter most.

Better token value: Seed 1.8

Core performance indexes

LLM Stats Score

59.7

#1 · 23 evals

Best

34.1

#99 · 56 evals

Reasoning

57.8

#1 · 18 evals

Best

33.5

#101 · 39 evals

Coding

51.7

#1 · 10 evals

Best

19.7

#105 · 4 evals

Agents

44.5

#2 · 12 evals

Best

14.7

#94 · 6 evals

Cost, coverage & limits

Benchmark wins

1 of 1

Best

0 of 1

Input price

$4.00 / M

$0.25 / M

Best

Output price

$20.00 / M

$2.00 / M

Best

Context window

1,000,000

Best

256,000

Capability indexes

Additional strengths measured across groups of related public benchmarks

4 shared

Index

Claude Opus 5.5

Seed 1.8

Math

42.5#5 · 3 evals

32.5#59 · 10 evals

Vision

42.8#1 · 5 evals

24.1#56 · 38 evals

Tool use

32.9#2 · 4 evals

6.4#149 · 2 evals

Multimodal

42.5#1 · 5 evals

27.4#41 · 32 evals

Conservative TrueSkill rating · higher is betterHow scores work

Individual benchmarks

31 reported for Claude Opus 5.5 · 57 for Seed 1.8

1 shared

Claude Opus 5.5 outperforms in 1 benchmarks (Humanity's Last Exam (with tools, text-only)), while Seed 1.8 is better at 0 benchmarks.

Claude Opus 5.5 significantly outperforms across most benchmarks.

Sun Sep 27 2026 • llm-stats.com

Human preference

Blind head-to-head votes and playground preference scores

Pricing Analysis

Price comparison per million tokens

Seed 1.8 costs less

For input processing, Claude Opus 5.5 ($4.00/1M tokens) is 16.0x more expensive than Seed 1.8 ($0.25/1M tokens).

For output processing, Claude Opus 5.5 ($20.00/1M tokens) is 10.0x more expensive than Seed 1.8 ($2.00/1M tokens).

In conclusion, Claude Opus 5.5 is more expensive than Seed 1.8.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers

Sun Sep 27 2026 • llm-stats.com

Claude Opus 5.5

Input tokens$4.00

Output tokens$20.00

Best providerAnthropic

Seed 1.8

Input tokens$0.25

Output tokens$2.00

Best providerDeepinfra

Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Claude Opus 5.5 accepts 1,000,000 input tokens compared to Seed 1.8's 256,000 tokens. Seed 1.8 can generate longer responses up to 256,000 tokens, while Claude Opus 5.5 is limited to 128,000 tokens.

Claude Opus 5.5

Input1,000,000 tokens

Output128,000 tokens

Seed 1.8

Input256,000 tokens

Output256,000 tokens

Sun Sep 27 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both Claude Opus 5.5 and Seed 1.8 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 1.8

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 1.8

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Opus 5.5 was released on 2026-09-22, while Seed 1.8 was released on 2026-02-17.

Claude Opus 5.5 is 7 months newer than Seed 1.8.

Claude Opus 5.5

Sep 22, 2026

5 days ago

7mo newer

Seed 1.8

Feb 17, 2026

7 months ago

Knowledge Cutoff

When training data ends

Claude Opus 5.5 has a documented knowledge cutoff of 2026-06-01, while Seed 1.8'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 1.8's cutoff date.

Claude Opus 5.5

Jun 2026

Seed 1.8

—

Provider Availability

Claude Opus 5.5 is available from Anthropic. Seed 1.8 is available from DeepInfra.

Claude Opus 5.5

Anthropic

Input Price:Input: $4.00/1MOutput Price:Output: $20.00/1M

Seed 1.8

Deepinfra

Input Price:Input: $0.25/1MOutput Price:Output: $2.00/1M

* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against Claude Opus 5.5 and Seed 1.8 side-by-side, then vote on the output you prefer.

Claude Opus 5.5

✓ Preferred

Seed 1.8

Open in Playground

FAQ

Common questions about Claude Opus 5.5 vs Seed 1.8.

Which is better, Claude Opus 5.5 or Seed 1.8?

Claude Opus 5.5 leads the LLM Stats Score 59.7 to 34.1. Claude Opus 5.5 is made by Anthropic and Seed 1.8 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 1.8 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 1.8 scores CountBench: 96.3%, AIME 2025: 94.3%, VLMsAreBlind: 93.0%, MMLU: 92.3%, AI2D: 89.1%.

Is Claude Opus 5.5 cheaper than Seed 1.8?

Seed 1.8 is 16.0x cheaper for input tokens. Claude Opus 5.5 costs $4.00/M input and $20.00/M output via anthropic. Seed 1.8 costs $0.25/M input and $2.00/M output via deepinfra.

What are the context window sizes for Claude Opus 5.5 and Seed 1.8?

Claude Opus 5.5 supports 1.0M tokens and Seed 1.8 supports 256K 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 1.8?

Key differences include LLM Stats Score (59.7 vs 34.1), context window (1.0M vs 256K), input pricing ($4.00 vs $0.25/M). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Opus 5.5 and Seed 1.8?

Claude Opus 5.5 is developed by Anthropic and Seed 1.8 is developed by ByteDance.

Claude Opus 5.5 vs Seed 1.8