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Grok-4 Heavy vs Kimi K2.8 Preview

Comparing Grok-4 Heavy and Kimi K2.8 Preview across benchmarks, pricing, and capabilities.

xAI · Moonshot AI · Updated for 2026

Which is better?

Grok-4 Heavy and Kimi K2.8 Preview trade strengths across price, capabilities, and technical limits. The better choice depends on the workload.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose Grok-4 Heavy

  • you are already invested in the xAI ecosystem

Choose Kimi K2.8 Preview

  • you are already invested in the Moonshot AI ecosystem

At a glance

The differences that matter most.

Grok-4 Heavy
xAI
Kimi K2.8 Preview
Moonshot AI
Benchmark wins
—
—
Input price
— / M
— / M
Output price
— / M
— / M
Context window
—
1,048,576

Individual benchmarks

6 reported for Grok-4 Heavy · 0 for Kimi K2.8 Preview

No common benchmarks found

Grok-4 Heavy and Kimi K2.8 Previewdon'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 Kimi K2.8 Preview specifies input context (1,048,576 tokens).

xAI
Grok-4 Heavy
Input- tokens
Output- tokens
Moonshot AI
Kimi K2.8 Preview
Input1,048,576 tokens
Output- tokens
Sun Sep 20 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both Grok-4 Heavy and Kimi K2.8 Preview support multimodal inputs.

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

Grok-4 Heavy

Text
Images
Audio
Video

Kimi K2.8 Preview

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.

Grok-4 Heavy

Proprietary

Closed source

Kimi K2.8 Preview

Proprietary

Closed source

Release Timeline

When each model was launched

Kimi K2.8 Preview was released on 2026-09-11, while Grok-4 Heavy's release date is not specified.

We can confirm Kimi K2.8 Preview's release timeline, but cannot make a direct age comparison without Grok-4 Heavy's release date.

Grok-4 Heavy

—

Kimi K2.8 Preview

Sep 11, 2026

1 weeks ago

Knowledge Cutoff

When training data ends

Grok-4 Heavy has a documented knowledge cutoff of 2024-12-31, while Kimi K2.8 Preview'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 K2.8 Preview's cutoff date.

Grok-4 Heavy

Dec 2024

Kimi K2.8 Preview

—

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against Grok-4 Heavy and Kimi K2.8 Preview side-by-side, then vote on the output you prefer.

Grok-4 Heavy
✓ Preferred
Kimi K2.8 Preview
Open in Playground

FAQ

Common questions about Grok-4 Heavy vs Kimi K2.8 Preview.

Which is better, Grok-4 Heavy or Kimi K2.8 Preview?

Grok-4 Heavy (xAI) and Kimi K2.8 Preview (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 Heavy compare to Kimi K2.8 Preview in benchmarks?

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 Grok-4 Heavy and Kimi K2.8 Preview?

Grok-4 Heavy supports an unknown number of tokens and Kimi K2.8 Preview supports 1.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

Who makes Grok-4 Heavy and Kimi K2.8 Preview?

Grok-4 Heavy is developed by xAI and Kimi K2.8 Preview is developed by Moonshot AI.

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