Model Comparison
GPT-5.6 Sol vs Grok-4 Fast ReasoningWhich is better in 2026?
Comparing GPT-5.6 Sol and Grok-4 Fast Reasoning across benchmarks, pricing, and capabilities.
Verdict: GPT-5.6 Sol vs Grok-4 Fast Reasoning — which is better?
GPT-5.6 Sol (by OpenAI) and Grok-4 Fast 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, Grok-4 Fast Reasoning is roughly 40.9x 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 GPT-5.6 Sol if…
- you want the most recent training data — it shipped Jul 2026
Choose Grok-4 Fast Reasoning if…
- cost matters — it's about 40.9x cheaper per token
- you process long inputs — it offers a 2,000,000 token context window
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.6 Sol and Grok-4 Fast 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 Sol ($5.00/1M tokens) is 25.0x more expensive than Grok-4 Fast Reasoning ($0.20/1M tokens).
For output processing, GPT-5.6 Sol ($30.00/1M tokens) is 60.0x more expensive than Grok-4 Fast Reasoning ($0.50/1M tokens).
In conclusion, GPT-5.6 Sol is more expensive than Grok-4 Fast Reasoning.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok-4 Fast Reasoning accepts 2,000,000 input tokens compared to GPT-5.6 Sol's 1,050,000 tokens. GPT-5.6 Sol can generate longer responses up to 128,000 tokens, while Grok-4 Fast Reasoning is limited to 30,000 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-5.6 Sol and Grok-4 Fast Reasoning support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.6 Sol
Grok-4 Fast 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 Sol was released on 2026-07-09, while Grok-4 Fast Reasoning was released on 2025-08-28.
GPT-5.6 Sol is 11 months newer than Grok-4 Fast Reasoning.
Jul 9, 2026
2 weeks ago
10mo newerAug 28, 2025
11 months ago
Knowledge Cutoff
When training data ends
GPT-5.6 Sol has a documented knowledge cutoff of 2026-02-16, while Grok-4 Fast Reasoning's cutoff date is not specified.
We can confirm GPT-5.6 Sol's training data extends to 2026-02-16, but cannot make a direct comparison without Grok-4 Fast Reasoning's cutoff date.
Feb 2026
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Provider Availability
GPT-5.6 Sol is available from OpenAI. Grok-4 Fast Reasoning is available from xAI.
GPT-5.6 Sol
Grok-4 Fast Reasoning
Outputs Comparison
Key Takeaways
GPT-5.6 Sol
View detailsOpenAI
No standout differentiators in the data we have for this pair.
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.6 Sol and Grok-4 Fast Reasoning side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.6 Sol vs Grok-4 Fast Reasoning.