Model Comparison

GPT-5.6 Luna vs Grok Code Fast 1Which is better in 2026?

Comparing GPT-5.6 Luna and Grok Code Fast 1 across benchmarks, pricing, and capabilities.

Verdict: GPT-5.6 Luna vs Grok Code Fast 1 — which is better?

GPT-5.6 Luna (by OpenAI) and Grok Code Fast 1 (by xAI) 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 Code Fast 1 is roughly 4.3x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

GPT-5.6 Luna also accepts a larger context window (1,050,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose GPT-5.6 Luna if…

  • you process long inputs — it offers a 1,050,000 token context window
  • you want the most recent training data — it shipped Jul 2026

Choose Grok Code Fast 1 if…

  • cost matters — it's about 4.3x cheaper per token

Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

GPT-5.6 Luna and Grok Code Fast 1don'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 Code Fast 1 costs less

For input processing, GPT-5.6 Luna ($1.00/1M tokens) is 5.0x more expensive than Grok Code Fast 1 ($0.20/1M tokens).

For output processing, GPT-5.6 Luna ($6.00/1M tokens) is 4.0x more expensive than Grok Code Fast 1 ($1.50/1M tokens).

In conclusion, GPT-5.6 Luna is more expensive than Grok Code Fast 1.*

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

Lowest available price from all providers
Tue Jul 21 2026 • llm-stats.com
OpenAI
GPT-5.6 Luna
Input tokens$1.00
Output tokens$6.00
Best providerOpenAI
xAI
Grok Code Fast 1
Input tokens$0.20
Output tokens$1.50
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

GPT-5.6 Luna accepts 1,050,000 input tokens compared to Grok Code Fast 1's 256,000 tokens. GPT-5.6 Luna can generate longer responses up to 128,000 tokens, while Grok Code Fast 1 is limited to 10,000 tokens.

OpenAI
GPT-5.6 Luna
Input1,050,000 tokens
Output128,000 tokens
xAI
Grok Code Fast 1
Input256,000 tokens
Output10,000 tokens
Tue Jul 21 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

GPT-5.6 Luna supports multimodal inputs, whereas Grok Code Fast 1 does not.

GPT-5.6 Luna can handle both text and other forms of data like images, making it suitable for multimodal applications.

GPT-5.6 Luna

Text
Images
Audio
Video

Grok Code Fast 1

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-5.6 Luna

Proprietary

Closed source

Grok Code Fast 1

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.6 Luna was released on 2026-07-09, while Grok Code Fast 1 was released on 2025-08-28.

GPT-5.6 Luna is 11 months newer than Grok Code Fast 1.

GPT-5.6 Luna

Jul 9, 2026

1 weeks ago

10mo newer
Grok Code Fast 1

Aug 28, 2025

10 months ago

Knowledge Cutoff

When training data ends

GPT-5.6 Luna has a documented knowledge cutoff of 2026-02-16, while Grok Code Fast 1's cutoff date is not specified.

We can confirm GPT-5.6 Luna's training data extends to 2026-02-16, but cannot make a direct comparison without Grok Code Fast 1's cutoff date.

GPT-5.6 Luna

Feb 2026

Grok Code Fast 1

—

Provider Availability

GPT-5.6 Luna is available from OpenAI. Grok Code Fast 1 is available from xAI.

GPT-5.6 Luna

openai logo
OpenAI
Input Price:Input: $1.00/1MOutput Price:Output: $6.00/1M

Grok Code Fast 1

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $1.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

OpenAI
Larger context window (1,050,000 tokens)
Supports multimodal inputs
xAI
Less expensive input tokens
Less expensive output tokens

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against GPT-5.6 Luna and Grok Code Fast 1 side-by-side, then vote on the output you prefer.

GPT-5.6 Luna
✓ Preferred
Grok Code Fast 1
Open in Playground
AI Model Comparison Table
Feature
OpenAI
GPT-5.6 Luna
xAI
Grok Code Fast 1

FAQ

Common questions about GPT-5.6 Luna vs Grok Code Fast 1.

Which is better, GPT-5.6 Luna or Grok Code Fast 1?

GPT-5.6 Luna (OpenAI) and Grok Code Fast 1 (xAI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-5.6 Luna compare to Grok Code Fast 1 in benchmarks?

GPT-5.6 Luna scores Connectors: 99.9%, HealthBench Consensus: 95.1%, GPQA: 92.3%, Search and Function-Calling: 89.7%, Capture-the-Flag Challenges (Internal): 85.2%. Grok Code Fast 1 scores SWE-Bench Verified: 70.8%.

Is GPT-5.6 Luna cheaper than Grok Code Fast 1?

Grok Code Fast 1 is 5.0x cheaper for input tokens. GPT-5.6 Luna costs $1.00/M input and $6.00/M output via openai. Grok Code Fast 1 costs $0.20/M input and $1.50/M output via xai.

What are the context window sizes for GPT-5.6 Luna and Grok Code Fast 1?

GPT-5.6 Luna supports 1.1M tokens and Grok Code Fast 1 supports 256K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5.6 Luna and Grok Code Fast 1?

Key differences include context window (1.1M vs 256K), input pricing ($1.00 vs $0.20/M), multimodal support (yes vs no). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5.6 Luna and Grok Code Fast 1?

GPT-5.6 Luna is developed by OpenAI and Grok Code Fast 1 is developed by xAI.

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