Model Comparison

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

Comparing Grok-4 Fast Reasoning and Kimi K2-Thinking-0905 across benchmarks, pricing, and capabilities.

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

Grok-4 Fast Reasoning (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.

On price, Grok-4 Fast Reasoning is roughly 3.1x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok-4 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose Grok-4 Fast Reasoning if…

  • cost matters — it's about 3.1x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window

Choose Kimi K2-Thinking-0905 if…

  • you want the most recent training data — it shipped Sep 2025
  • you need open weights you can self-host or fine-tune
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Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

Grok-4 Fast Reasoning and Kimi K2-Thinking-0905don't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Grok-4 Fast Reasoning costs less

For input processing, Grok-4 Fast Reasoning ($0.20/1M tokens) is 2.3x cheaper than Kimi K2-Thinking-0905 ($0.47/1M tokens).

For output processing, Grok-4 Fast Reasoning ($0.50/1M tokens) is 4.0x cheaper than Kimi K2-Thinking-0905 ($2.00/1M tokens).

In conclusion, Kimi K2-Thinking-0905 is more expensive than Grok-4 Fast Reasoning.*

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

Lowest available price from all providers
Fri Jun 12 2026 • llm-stats.com
xAI
Grok-4 Fast Reasoning
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Moonshot AI
Kimi K2-Thinking-0905
Input tokens$0.47
Output tokens$2.00
Best providerDeepinfra
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok-4 Fast Reasoning accepts 2,000,000 input tokens compared to Kimi K2-Thinking-0905's 262,144 tokens. Kimi K2-Thinking-0905 can generate longer responses up to 262,144 tokens, while Grok-4 Fast Reasoning is limited to 30,000 tokens.

xAI
Grok-4 Fast Reasoning
Input2,000,000 tokens
Output30,000 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 Fast Reasoning supports multimodal inputs, whereas Kimi K2-Thinking-0905 does not.

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

Grok-4 Fast Reasoning

Text
Images
Audio
Video

Kimi K2-Thinking-0905

Text
Images
Audio
Video

License

Usage and distribution terms

Grok-4 Fast Reasoning 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 Fast Reasoning

Proprietary

Closed source

Kimi K2-Thinking-0905

MIT

Open weights

Release Timeline

When each model was launched

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

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

Grok-4 Fast Reasoning

Aug 28, 2025

9 months ago

Kimi K2-Thinking-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

Provider Availability

Grok-4 Fast Reasoning is available from xAI. Kimi K2-Thinking-0905 is available from DeepInfra, Novita, Fireworks.

Grok-4 Fast Reasoning

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M

Kimi K2-Thinking-0905

deepinfra logo
Deepinfra
Input Price:Input: $0.47/1MOutput Price:Output: $2.00/1M
novita logo
Novita
Input Price:Input: $0.48/1MOutput Price:Output: $2.00/1M
fireworks logo
Fireworks
Input Price:Input: $0.60/1MOutput Price:Output: $2.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

xAI
Larger context window (2,000,000 tokens)
Supports multimodal inputs
Less expensive input tokens
Less expensive output tokens
Moonshot AI
Has open weights

Detailed Comparison

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

FAQ

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

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

Grok-4 Fast Reasoning (xAI) and Kimi K2-Thinking-0905 (Moonshot AI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

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

Kimi K2-Thinking-0905 scores AIME 2025: 100.0%, HMMT 2025: 97.5%, MMLU-Redux: 94.4%, FRAMES: 87.0%, MMLU-Pro: 84.6%.

Is Grok-4 Fast Reasoning cheaper than Kimi K2-Thinking-0905?

Grok-4 Fast Reasoning is 2.3x cheaper for input tokens. Grok-4 Fast Reasoning costs $0.20/M input and $0.50/M output via xai. Kimi K2-Thinking-0905 costs $0.47/M input and $2.00/M output via deepinfra.

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

Grok-4 Fast Reasoning supports 2.0M 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 Fast Reasoning and Kimi K2-Thinking-0905?

Key differences include context window (2.0M vs 262K), input pricing ($0.20 vs $0.47/M), multimodal support (yes vs no), licensing (Proprietary vs MIT). See the full comparison above for benchmark-by-benchmark results.

Who makes Grok-4 Fast Reasoning and Kimi K2-Thinking-0905?

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

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