GPT-5 Codex vs OpenAI o3

Compare GPT-5 Codex and OpenAI o3, both from OpenAI, tested across 50 shared challenges. Updated April 2026.

Which is better, GPT-5 Codex or OpenAI o3?

GPT-5 Codex and OpenAI o3 are both competitive models. Compare their real outputs side by side below.

Key Differences Between GPT-5 Codex and OpenAI o3

GPT-5 Codex is made by openai while OpenAI o3 is from openai.

Our Verdict
GPT-5 Codex
GPT-5 Codex
OpenAI o3
OpenAI o3

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
100%

GPT-5 Codex uses 14.6x more emoji

GPT-5 Codex
OpenAI o3
64%Vocabulary68%
17wSentence Length14w
0.38Hedging0.26
2.3Bold0.7
3.5Lists3.0
0.15Emoji0.00
0.49Headings0.38
0.05Transitions0.12
Based on 13 + 16 text responses
vs

Ask them anything yourself

GPT-5 CodexOpenAI o3

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
FAQ

Common questions