Model Comparison

Grok-4 Heavy vs Kimi K2-Thinking-0905Which is better in 2026?

Both models are evenly matched across the benchmarks.

Verdict: Grok-4 Heavy vs Kimi K2-Thinking-0905 — which is better?

Grok-4 Heavy (by xAI) and Kimi K2-Thinking-0905 (by Moonshot AI) 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.

Grok-4 Heavy outperforms in 1 benchmarks (GPQA), while Kimi K2-Thinking-0905 is better at 1 benchmark (Humanity's Last Exam). Both models are evenly matched across the benchmarks.

Choose Grok-4 Heavy if…

  • you are already invested in the xAI ecosystem

Choose Kimi K2-Thinking-0905 if…

  • you want the strongest raw capability — it leads on 2 of 3 shared benchmarks
  • you need open weights you can self-host or fine-tune
Want to compare interactively?Try the playground

Performance Benchmarks

Comparative analysis across standard metrics

3 benchmarks

Grok-4 Heavy outperforms in 1 benchmarks (GPQA), while Kimi K2-Thinking-0905 is better at 1 benchmark (Humanity's Last Exam).

Both models are evenly matched across the benchmarks.

Fri Jun 12 2026 • llm-stats.com

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only Kimi K2-Thinking-0905 specifies input context (262,144 tokens). Only Kimi K2-Thinking-0905 specifies output context (262,144 tokens).

xAI
Grok-4 Heavy
Input- tokens
Output- tokens
Moonshot AI
Kimi K2-Thinking-0905
Input262,144 tokens
Output262,144 tokens
Fri Jun 12 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Grok-4 Heavy supports multimodal inputs, whereas Kimi K2-Thinking-0905 does not.

Grok-4 Heavy can handle both text and other forms of data like images, making it suitable for multimodal applications.

Grok-4 Heavy

Text
Images
Audio
Video

Kimi K2-Thinking-0905

Text
Images
Audio
Video

License

Usage and distribution terms

Grok-4 Heavy is licensed under a proprietary license, while Kimi K2-Thinking-0905 uses MIT.

License differences may affect how you can use these models in commercial or open-source projects.

Grok-4 Heavy

Proprietary

Closed source

Kimi K2-Thinking-0905

MIT

Open weights

Release Timeline

When each model was launched

Kimi K2-Thinking-0905 was released on 2025-09-05, while Grok-4 Heavy's release date is not specified.

We can confirm Kimi K2-Thinking-0905's release timeline, but cannot make a direct age comparison without Grok-4 Heavy's release date.

Grok-4 Heavy

—

Kimi K2-Thinking-0905

Sep 5, 2025

9 months ago

Knowledge Cutoff

When training data ends

Grok-4 Heavy has a documented knowledge cutoff of 2024-12-31, while Kimi K2-Thinking-0905's cutoff date is not specified.

We can confirm Grok-4 Heavy's training data extends to 2024-12-31, but cannot make a direct comparison without Kimi K2-Thinking-0905's cutoff date.

Grok-4 Heavy

Dec 2024

Kimi K2-Thinking-0905

—

Outputs Comparison

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Key Takeaways

xAI
Supports multimodal inputs
Higher GPQA score (88.4% vs 84.5%)
Moonshot AI
Larger context window (262,144 tokens)
Has open weights
Higher Humanity's Last Exam score (51.0% vs 50.7%)

Detailed Comparison

AI Model Comparison Table
Feature
xAI
Grok-4 Heavy
Moonshot AI
Kimi K2-Thinking-0905

FAQ

Common questions about Grok-4 Heavy vs Kimi K2-Thinking-0905.

Which is better, Grok-4 Heavy or Kimi K2-Thinking-0905?

Both models are evenly matched across the benchmarks. Grok-4 Heavy is made by xAI and Kimi K2-Thinking-0905 is made by Moonshot AI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does Grok-4 Heavy compare to Kimi K2-Thinking-0905 in benchmarks?

Grok-4 Heavy scores AIME 2025: 100.0%, HMMT25: 96.7%, GPQA: 88.4%, LiveCodeBench: 79.4%, USAMO25: 61.9%. Kimi K2-Thinking-0905 scores AIME 2025: 100.0%, HMMT 2025: 97.5%, MMLU-Redux: 94.4%, FRAMES: 87.0%, MMLU-Pro: 84.6%.

What are the context window sizes for Grok-4 Heavy and Kimi K2-Thinking-0905?

Grok-4 Heavy supports an unknown number of tokens and Kimi K2-Thinking-0905 supports 262K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between Grok-4 Heavy and Kimi K2-Thinking-0905?

Key differences include multimodal support (yes vs no), licensing (Proprietary vs MIT). See the full comparison above for benchmark-by-benchmark results.

Who makes Grok-4 Heavy and Kimi K2-Thinking-0905?

Grok-4 Heavy is developed by xAI and Kimi K2-Thinking-0905 is developed by Moonshot AI.

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