Model Comparison

Grok 4 Fast vs Kimi K2-Instruct-0905

Grok 4 Fast significantly outperforms across most benchmarks.

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Performance Benchmarks

Comparative analysis across standard metrics

6 benchmarks

Grok 4 Fast outperforms in 6 benchmarks (AIME 2025, GPQA, HMMT 2025, Humanity's Last Exam, LiveCodeBench, SimpleQA), while Kimi K2-Instruct-0905 is better at 0 benchmarks.

Grok 4 Fast significantly outperforms across most benchmarks.

Thu Jun 04 2026 • llm-stats.com

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only Grok 4 Fast specifies input context (2,000,000 tokens). Only Grok 4 Fast specifies output context (30,000 tokens).

xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
Moonshot AI
Kimi K2-Instruct-0905
Input- tokens
Output- tokens
Thu Jun 04 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Grok 4 Fast supports multimodal inputs, whereas Kimi K2-Instruct-0905 does not.

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

Grok 4 Fast

Text
Images
Audio
Video

Kimi K2-Instruct-0905

Text
Images
Audio
Video

License

Usage and distribution terms

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

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

Grok 4 Fast

Proprietary

Closed source

Kimi K2-Instruct-0905

MIT

Open weights

Release Timeline

When each model was launched

Grok 4 Fast was released on 2025-08-28, while Kimi K2-Instruct-0905 was released on 2025-09-05.

Kimi K2-Instruct-0905 is 0 month newer than Grok 4 Fast.

Grok 4 Fast

Aug 28, 2025

9 months ago

Kimi K2-Instruct-0905

Sep 5, 2025

9 months ago

1w newer

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

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Key Takeaways

xAI
Larger context window (2,000,000 tokens)
Supports multimodal inputs
Higher AIME 2025 score (92.0% vs 49.5%)
Higher GPQA score (85.7% vs 75.1%)
Higher HMMT 2025 score (93.3% vs 38.8%)
Higher Humanity's Last Exam score (20.0% vs 4.7%)
Higher LiveCodeBench score (80.0% vs 53.7%)
Higher SimpleQA score (95.0% vs 31.0%)
Moonshot AI
Has open weights

Detailed Comparison

AI Model Comparison Table
Feature
xAI
Grok 4 Fast
Moonshot AI
Kimi K2-Instruct-0905

FAQ

Common questions about Grok 4 Fast vs Kimi K2-Instruct-0905.

Which is better, Grok 4 Fast or Kimi K2-Instruct-0905?

Grok 4 Fast significantly outperforms across most benchmarks. Grok 4 Fast is made by xAI and Kimi K2-Instruct-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 Fast compare to Kimi K2-Instruct-0905 in benchmarks?

Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%. Kimi K2-Instruct-0905 scores MATH-500: 97.4%, MMLU-Redux: 92.7%, IFEval: 89.8%, AutoLogi: 89.5%, MMLU: 89.5%.

What are the context window sizes for Grok 4 Fast and Kimi K2-Instruct-0905?

Grok 4 Fast supports 2.0M tokens and Kimi K2-Instruct-0905 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 Grok 4 Fast and Kimi K2-Instruct-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 Fast and Kimi K2-Instruct-0905?

Grok 4 Fast is developed by xAI and Kimi K2-Instruct-0905 is developed by Moonshot AI.