GPT-5 Codex vs GPT OSS 120B

Compare GPT-5 Codex and GPT OSS 120B, both from OpenAI, tested across 45 shared challenges. Updated April 2026.

Which is better, GPT-5 Codex or GPT OSS 120B?

GPT-5 Codex and GPT OSS 120B are both competitive models. Compare their real outputs side by side below.

Key Differences Between GPT-5 Codex and GPT OSS 120B

GPT-5 Codex is made by openai while GPT OSS 120B is from openai.

Our Verdict
GPT-5 Codex
GPT-5 Codex
GPT OSS 120B
GPT OSS 120B

No community votes yet. On paper, these are closely matched - try both with your actual task to see which fits your workflow.

Too close to call
Writing DNA

Style Comparison

Similarity
99%

GPT OSS 120B uses 3.2x more bold

GPT-5 Codex
GPT OSS 120B
64%Vocabulary52%
17wSentence Length19w
0.38Hedging0.28
2.3Bold7.4
3.5Lists1.8
0.15Emoji0.15
0.49Headings0.73
0.05Transitions0.17
Based on 13 + 21 text responses
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GPT-5 CodexGPT OSS 120B

279 AI models invented the same fake scientist.

We read every word. 250 models. 2.14 million words. This is what we found.

AI Hallucination Index 2026
Free preview13 of 58 slides
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