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ChatGPT-4o (March 2025) vs GPT-5 Codex

Compare ChatGPT-4o (March 2025) and GPT-5 Codex, both from OpenAI, tested across 32 shared challenges. Updated April 2026.

Which is better, ChatGPT-4o (March 2025) or GPT-5 Codex?

ChatGPT-4o (March 2025) and GPT-5 Codex are both competitive models. Compare their real outputs side by side below.

Key Differences Between ChatGPT-4o (March 2025) and GPT-5 Codex

ChatGPT-4o (March 2025) is made by openai while GPT-5 Codex is from openai.

Our Verdict
ChatGPT-4o (March 2025)
ChatGPT-4o (March 2025)
GPT-5 Codex
GPT-5 Codex

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
93%

ChatGPT-4o (March 2025) uses 6.5x more emoji

ChatGPT-4o (March 2025)
GPT-5 Codex
55%Vocabulary64%
24wSentence Length17w
0.52Hedging0.38
3.3Bold2.3
6.0Lists3.5
0.94Emoji0.15
0.63Headings0.49
0.05Transitions0.05
Based on 15 + 13 text responses
vs

Ask them anything yourself

ChatGPT-4o (March 2025)GPT-5 Codex

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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