Model Comparison

Grok-4 Fast Reasoning vs Kimi K3Which is better in 2026?

Comparing Grok-4 Fast Reasoning and Kimi K3 across benchmarks, pricing, and capabilities.

Verdict: Grok-4 Fast Reasoning vs Kimi K3 — which is better?

Grok-4 Fast Reasoning (by xAI) and Kimi K3 (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 21.8x 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 21.8x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window

Choose Kimi K3 if…

  • you want the most recent training data — it shipped Jul 2026

Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

Grok-4 Fast Reasoning and Kimi K3don'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 15.0x cheaper than Kimi K3 ($3.00/1M tokens).

For output processing, Grok-4 Fast Reasoning ($0.50/1M tokens) is 30.0x cheaper than Kimi K3 ($15.00/1M tokens).

In conclusion, Kimi K3 is more expensive than Grok-4 Fast Reasoning.*

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

Lowest available price from all providers
Sun Jul 26 2026 • llm-stats.com
xAI
Grok-4 Fast Reasoning
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Moonshot AI
Kimi K3
Input tokens$3.00
Output tokens$15.00
Best providerUnknown Organization
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 K3's 1,048,576 tokens. Kimi K3 can generate longer responses up to 1,048,576 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 K3
Input1,048,576 tokens
Output1,048,576 tokens
Sun Jul 26 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Grok-4 Fast Reasoning and Kimi K3 support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

Grok-4 Fast Reasoning

Text
Images
Audio
Video

Kimi K3

Text
Images
Audio
Video

Release Timeline

When each model was launched

Grok-4 Fast Reasoning was released on 2025-08-28, while Kimi K3 was released on 2026-07-16.

Kimi K3 is 11 months newer than Grok-4 Fast Reasoning.

Grok-4 Fast Reasoning

Aug 28, 2025

11 months ago

Kimi K3

Jul 16, 2026

1 weeks ago

10mo 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 K3 is available from Moonshot AI.

Grok-4 Fast Reasoning

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

Kimi K3

moonshot logo
Unknown Organization
Input Price:Input: $3.00/1MOutput Price:Output: $15.00/1M
* 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)
Less expensive input tokens
Less expensive output tokens
Moonshot AI
Has open weights

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against Grok-4 Fast Reasoning and Kimi K3 side-by-side, then vote on the output you prefer.

Grok-4 Fast Reasoning
✓ Preferred
Kimi K3
Open in Playground
AI Model Comparison Table
Feature
xAI
Grok-4 Fast Reasoning
Moonshot AI
Kimi K3

FAQ

Common questions about Grok-4 Fast Reasoning vs Kimi K3.

Which is better, Grok-4 Fast Reasoning or Kimi K3?

Grok-4 Fast Reasoning (xAI) and Kimi K3 (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 K3 in benchmarks?

Kimi K3 scores MathVision: 97.8%, DeepSearchQA: 95.0%, GPQA: 93.5%, CharXiv-R: 91.3%, BrowseComp: 91.2%.

Is Grok-4 Fast Reasoning cheaper than Kimi K3?

Grok-4 Fast Reasoning is 15.0x cheaper for input tokens. Grok-4 Fast Reasoning costs $0.20/M input and $0.50/M output via xai. Kimi K3 costs $3.00/M input and $15.00/M output via moonshot.

What are the context window sizes for Grok-4 Fast Reasoning and Kimi K3?

Grok-4 Fast Reasoning supports 2.0M tokens and Kimi K3 supports 1.0M 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 K3?

Key differences include context window (2.0M vs 1.0M), input pricing ($0.20 vs $3.00/M), licensing (Proprietary vs Unknown). See the full comparison above for benchmark-by-benchmark results.

Who makes Grok-4 Fast Reasoning and Kimi K3?

Grok-4 Fast Reasoning is developed by xAI and Kimi K3 is developed by Moonshot AI.

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