Model Comparison
GPT-5.1 Codex vs Grok-4 Fast Non-ReasoningWhich is better in 2026?
Comparing GPT-5.1 Codex and Grok-4 Fast Non-Reasoning across benchmarks, pricing, and capabilities.
Verdict: GPT-5.1 Codex vs Grok-4 Fast Non-Reasoning — which is better?
GPT-5.1 Codex (by OpenAI) and Grok-4 Fast Non-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 Non-Reasoning is roughly 12.5x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Grok-4 Fast Non-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-5.1 Codex if…
- you want the most recent training data — it shipped Nov 2025
Choose Grok-4 Fast Non-Reasoning if…
- cost matters — it's about 12.5x cheaper per token
- you process long inputs — it offers a 2,000,000 token context window
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.1 Codex and Grok-4 Fast Non-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-5.1 Codex ($1.25/1M tokens) is 6.3x more expensive than Grok-4 Fast Non-Reasoning ($0.20/1M tokens).
For output processing, GPT-5.1 Codex ($10.00/1M tokens) is 20.0x more expensive than Grok-4 Fast Non-Reasoning ($0.50/1M tokens).
In conclusion, GPT-5.1 Codex is more expensive than Grok-4 Fast Non-Reasoning.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok-4 Fast Non-Reasoning accepts 2,000,000 input tokens compared to GPT-5.1 Codex's 400,000 tokens. GPT-5.1 Codex can generate longer responses up to 128,000 tokens, while Grok-4 Fast Non-Reasoning is limited to 30,000 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-5.1 Codex and Grok-4 Fast Non-Reasoning support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.1 Codex
Grok-4 Fast Non-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-5.1 Codex was released on 2025-11-19, while Grok-4 Fast Non-Reasoning was released on 2025-08-28.
GPT-5.1 Codex is 3 months newer than Grok-4 Fast Non-Reasoning.
Nov 19, 2025
7 months ago
2mo newerAug 28, 2025
10 months ago
Knowledge Cutoff
When training data ends
GPT-5.1 Codex has a documented knowledge cutoff of 2024-09-30, while Grok-4 Fast Non-Reasoning's cutoff date is not specified.
We can confirm GPT-5.1 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without Grok-4 Fast Non-Reasoning's cutoff date.
Sep 2024
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Provider Availability
GPT-5.1 Codex is available from OpenAI. Grok-4 Fast Non-Reasoning is available from xAI.
GPT-5.1 Codex
Grok-4 Fast Non-Reasoning
Outputs Comparison
Key Takeaways
No standout differentiators in the data we have for this pair.
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.1 Codex and Grok-4 Fast Non-Reasoning side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.1 Codex vs Grok-4 Fast Non-Reasoning.