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Claude Opus 5.5 vs Grok-4 Heavy

Claude Opus 5.5 leads the LLM Stats Score 59.7 to 40.7.

Anthropic · xAI · Updated for 2026

Which is better?

Claude Opus 5.5 leads the overall LLM Stats Score 59.7 to 40.7, ranking #1 overall.

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

Choose Grok-4 Heavy

  • you are already invested in the xAI ecosystem

At a glance

The differences that matter most.

Claude Opus 5.5
Anthropic
Grok-4 Heavy
xAI
Core performance indexes
LLM Stats Score
59.7
#1
40.7
#59
Reasoning
57.8
#1
39.0
#63
Coding
51.7
#1
17.7
#121
Cost, coverage & limits
Benchmark wins
—
—
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

1 shared
Index
Claude Opus 5.5
Grok-4 Heavy
Math
42.5#5
41.5#7
Conservative TrueSkill rating · higher is betterHow scores work

Individual benchmarks

31 reported for Claude Opus 5.5 · 6 for Grok-4 Heavy

No common benchmarks found

Claude Opus 5.5 and Grok-4 Heavydon'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 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
xAI
Grok-4 Heavy
Input- tokens
Output- tokens
Tue Sep 22 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both Claude Opus 5.5 and Grok-4 Heavy 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

Grok-4 Heavy

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

Grok-4 Heavy

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Opus 5.5 was released on 2026-09-22, while Grok-4 Heavy's release date is not specified.

We can confirm Claude Opus 5.5's release timeline, but cannot make a direct age comparison without Grok-4 Heavy's release date.

Claude Opus 5.5

Sep 22, 2026

0 days ago

Grok-4 Heavy

—

Knowledge Cutoff

When training data ends

Claude Opus 5.5 has a knowledge cutoff of 2026-06-01, while Grok-4 Heavy has a cutoff of 2024-12-31.

Claude Opus 5.5 has more recent training data (up to 2026-06-01), making it potentially better informed about events through that date compared to Grok-4 Heavy (2024-12-31).

Claude Opus 5.5

Jun 2026

1.5 yr newer
Grok-4 Heavy

Dec 2024

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against Claude Opus 5.5 and Grok-4 Heavy side-by-side, then vote on the output you prefer.

Claude Opus 5.5
✓ Preferred
Grok-4 Heavy
Open in Playground

FAQ

Common questions about Claude Opus 5.5 vs Grok-4 Heavy.

Which is better, Claude Opus 5.5 or Grok-4 Heavy?

Claude Opus 5.5 leads the LLM Stats Score 59.7 to 40.7. Claude Opus 5.5 is made by Anthropic and Grok-4 Heavy is made by xAI. 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 Grok-4 Heavy 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%. Grok-4 Heavy scores AIME 2025: 100.0%, HMMT25: 96.7%, GPQA: 88.4%, LiveCodeBench: 79.4%, USAMO25: 61.9%.

What are the context window sizes for Claude Opus 5.5 and Grok-4 Heavy?

Claude Opus 5.5 supports 1.0M tokens and Grok-4 Heavy 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 Grok-4 Heavy?

Key differences include LLM Stats Score (59.7 vs 40.7). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Opus 5.5 and Grok-4 Heavy?

Claude Opus 5.5 is developed by Anthropic and Grok-4 Heavy is developed by xAI.

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