Model Comparison
GPT-5.6 Luna vs Grok-4.20 Beta ReasoningWhich is better in 2026?
Comparing GPT-5.6 Luna and Grok-4.20 Beta Reasoning across benchmarks, pricing, and capabilities.
Verdict: GPT-5.6 Luna vs Grok-4.20 Beta Reasoning — which is better?
GPT-5.6 Luna (by OpenAI) and Grok-4.20 Beta Reasoning (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, GPT-5.6 Luna is roughly 1.3x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Grok-4.20 Beta Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Choose GPT-5.6 Luna if…
- cost matters — it's about 1.3x cheaper per token
- you want the most recent training data — it shipped Jul 2026
Choose Grok-4.20 Beta Reasoning if…
- you process long inputs — it offers a 2,000,000 token context window
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.6 Luna and Grok-4.20 Beta Reasoningdon'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
For input processing, GPT-5.6 Luna ($1.00/1M tokens) is 2.0x cheaper than Grok-4.20 Beta Reasoning ($2.00/1M tokens).
For output processing, GPT-5.6 Luna ($6.00/1M tokens) costs the same as Grok-4.20 Beta Reasoning ($6.00/1M tokens).
In conclusion, Grok-4.20 Beta Reasoning is more expensive than GPT-5.6 Luna.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok-4.20 Beta Reasoning accepts 2,000,000 input tokens compared to GPT-5.6 Luna's 1,050,000 tokens. GPT-5.6 Luna can generate longer responses up to 128,000 tokens, while Grok-4.20 Beta Reasoning is limited to 30,000 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-5.6 Luna and Grok-4.20 Beta Reasoning support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.6 Luna
Grok-4.20 Beta Reasoning
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
GPT-5.6 Luna was released on 2026-07-09, while Grok-4.20 Beta Reasoning was released on 2026-03-09.
GPT-5.6 Luna is 4 months newer than Grok-4.20 Beta Reasoning.
Jul 9, 2026
2 weeks ago
4mo newerMar 9, 2026
4 months ago
Knowledge Cutoff
When training data ends
GPT-5.6 Luna has a documented knowledge cutoff of 2026-02-16, while Grok-4.20 Beta Reasoning'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-4.20 Beta Reasoning's cutoff date.
Feb 2026
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Provider Availability
GPT-5.6 Luna is available from OpenAI. Grok-4.20 Beta Reasoning is available from xAI.
GPT-5.6 Luna
Grok-4.20 Beta Reasoning
Outputs Comparison
Key Takeaways
GPT-5.6 Luna
View detailsOpenAI
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.6 Luna and Grok-4.20 Beta Reasoning side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.6 Luna vs Grok-4.20 Beta Reasoning.