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GPT-6 Luna vs Grok 4 Fast

GPT-6 Luna leads the LLM Stats Score 44.5 to 31.7. GPT-6 Luna is 1.4x cheaper per token.

OpenAI · xAI · Updated for 2026

Which is better?

GPT-6 Luna leads the overall LLM Stats Score 44.5 to 31.7, ranking #41 overall.

On price, GPT-6 Luna is roughly 1.4x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

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

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

Choose GPT-6 Luna

  • overall performance matters — it scores 44.5 and ranks #41 on LLM Stats
  • your work emphasizes reasoning and agents — it leads those capability indexes
  • cost matters — it's about 1.4x cheaper per token
  • you want the most recent training data — it shipped Sep 2026

Choose Grok 4 Fast

  • you process long inputs — it offers a 2,000,000 token context window

At a glance

The differences that matter most.

GPT-6 Luna
OpenAI
Grok 4 Fast
xAI
Core performance indexes
LLM Stats Score
44.5
#41
31.7
#116
Reasoning
40.0
#58
30.7
#120
Coding
31.4
#47
18.1
#118
Agents
31.8
#30
3.0
#167
Cost, coverage & limits
Benchmark wins
—
—
Input price
$0.10 / M
$0.20 / M
Output price
$0.50 / M
$0.50 / M
Context window
1,050,000
2,000,000

Individual benchmarks

5 reported for GPT-6 Luna · 7 for Grok 4 Fast

No common benchmarks found

GPT-6 Luna and Grok 4 Fastdon'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

Pricing Analysis

Price comparison per million tokens

GPT-6 Luna costs less

For input processing, GPT-6 Luna ($0.10/1M tokens) is 2.0x cheaper than Grok 4 Fast ($0.20/1M tokens).

For output processing, GPT-6 Luna ($0.50/1M tokens) costs the same as Grok 4 Fast ($0.50/1M tokens).

In conclusion, Grok 4 Fast is more expensive than GPT-6 Luna.*

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

Lowest available price from all providers
Tue Sep 22 2026 • llm-stats.com
OpenAI
GPT-6 Luna
Input tokens$0.10
Output tokens$0.50
Best providerOpenAI
xAI
Grok 4 Fast
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok 4 Fast accepts 2,000,000 input tokens compared to GPT-6 Luna's 1,050,000 tokens. GPT-6 Luna can generate longer responses up to 128,000 tokens, while Grok 4 Fast is limited to 30,000 tokens.

OpenAI
GPT-6 Luna
Input1,050,000 tokens
Output128,000 tokens
xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
Tue Sep 22 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both GPT-6 Luna and Grok 4 Fast support multimodal inputs.

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

GPT-6 Luna

Text
Images
Audio
Video

Grok 4 Fast

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.

GPT-6 Luna

Proprietary

Closed source

Grok 4 Fast

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-6 Luna was released on 2026-09-22, while Grok 4 Fast was released on 2025-08-28.

GPT-6 Luna is 13 months newer than Grok 4 Fast.

GPT-6 Luna

Sep 22, 2026

0 days ago

1.1yr newer
Grok 4 Fast

Aug 28, 2025

1.1 years ago

Knowledge Cutoff

When training data ends

GPT-6 Luna has a documented knowledge cutoff of 2026-05-18, while Grok 4 Fast's cutoff date is not specified.

We can confirm GPT-6 Luna's training data extends to 2026-05-18, but cannot make a direct comparison without Grok 4 Fast's cutoff date.

GPT-6 Luna

May 2026

Grok 4 Fast

—

Provider Availability

GPT-6 Luna is available from OpenAI. Grok 4 Fast is available from xAI.

GPT-6 Luna

openai logo
OpenAI
Input Price:Input: $0.10/1MOutput Price:Output: $0.50/1M

Grok 4 Fast

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against GPT-6 Luna and Grok 4 Fast side-by-side, then vote on the output you prefer.

GPT-6 Luna
✓ Preferred
Grok 4 Fast
Open in Playground

FAQ

Common questions about GPT-6 Luna vs Grok 4 Fast.

Which is better, GPT-6 Luna or Grok 4 Fast?

GPT-6 Luna leads the LLM Stats Score 44.5 to 31.7. GPT-6 Luna is made by OpenAI and Grok 4 Fast is made by xAI. The best choice depends on your use case — compare their capability indexes, individual benchmarks, pricing, and limits above.

How does GPT-6 Luna compare to Grok 4 Fast in benchmarks?

GPT-6 Luna scores DeepSWE 1.1: 66.6%, OSWorld 2.0: 52.7%, Agents' Last Exam: 50.9%, FrontierCode 1.1: 42.4%, AutomationBench v1.0.6: 20.7%. Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%.

Is GPT-6 Luna cheaper than Grok 4 Fast?

GPT-6 Luna is 2.0x cheaper for input tokens. GPT-6 Luna costs $0.10/M input and $0.50/M output via openai. Grok 4 Fast costs $0.20/M input and $0.50/M output via xai.

What are the context window sizes for GPT-6 Luna and Grok 4 Fast?

GPT-6 Luna supports 1.1M tokens and Grok 4 Fast supports 2.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-6 Luna and Grok 4 Fast?

Key differences include LLM Stats Score (44.5 vs 31.7), context window (1.1M vs 2.0M), input pricing ($0.10 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-6 Luna and Grok 4 Fast?

GPT-6 Luna is developed by OpenAI and Grok 4 Fast is developed by xAI.

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