Model Comparison

GPT-5 Codex vs Grok Code Fast 1

GPT-5 Codex significantly outperforms across most benchmarks.

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Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

GPT-5 Codex outperforms in 1 benchmarks (SWE-Bench Verified), while Grok Code Fast 1 is better at 0 benchmarks.

GPT-5 Codex significantly outperforms across most benchmarks.

Sun May 31 2026 • llm-stats.com

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only Grok Code Fast 1 specifies input context (256,000 tokens). Only Grok Code Fast 1 specifies output context (10,000 tokens).

OpenAI
GPT-5 Codex
Input- tokens
Output- tokens
xAI
Grok Code Fast 1
Input256,000 tokens
Output10,000 tokens
Sun May 31 2026 • llm-stats.com

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-5 Codex

Proprietary

Closed source

Grok Code Fast 1

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5 Codex was released on 2025-09-15, while Grok Code Fast 1 was released on 2025-08-28.

GPT-5 Codex is 1 month newer than Grok Code Fast 1.

GPT-5 Codex

Sep 15, 2025

8 months ago

2w newer
Grok Code Fast 1

Aug 28, 2025

9 months ago

Knowledge Cutoff

When training data ends

GPT-5 Codex has a documented knowledge cutoff of 2024-09-30, while Grok Code Fast 1's cutoff date is not specified.

We can confirm GPT-5 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without Grok Code Fast 1's cutoff date.

GPT-5 Codex

Sep 2024

Grok Code Fast 1

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Outputs Comparison

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Key Takeaways

OpenAI
Higher SWE-Bench Verified score (74.5% vs 70.8%)
xAI
Larger context window (256,000 tokens)

Detailed Comparison

AI Model Comparison Table
Feature
OpenAI
GPT-5 Codex
xAI
Grok Code Fast 1

FAQ

Common questions about GPT-5 Codex vs Grok Code Fast 1.

Which is better, GPT-5 Codex or Grok Code Fast 1?

GPT-5 Codex significantly outperforms across most benchmarks. GPT-5 Codex is made by OpenAI and Grok Code Fast 1 is made by xAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5 Codex compare to Grok Code Fast 1 in benchmarks?

GPT-5 Codex scores SWE-Bench Verified: 74.5%. Grok Code Fast 1 scores SWE-Bench Verified: 70.8%.

What are the context window sizes for GPT-5 Codex and Grok Code Fast 1?

GPT-5 Codex supports an unknown number of 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.

Who makes GPT-5 Codex and Grok Code Fast 1?

GPT-5 Codex is developed by OpenAI and Grok Code Fast 1 is developed by xAI.