Claude 3 Opus vs GPT-5 Codex

Compare Claude 3 Opus by Anthropic against GPT-5 Codex by OpenAI, tested across 11 shared challenges. Updated April 2026.

Which is better, Claude 3 Opus or GPT-5 Codex?

Claude 3 Opus and GPT-5 Codex are both competitive models. Compare their real outputs side by side below.

Key Differences Between Claude 3 Opus and GPT-5 Codex

Claude 3 Opus is made by anthropic while GPT-5 Codex is from openai.

Our Verdict
Claude 3 Opus
Claude 3 Opus
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
98%

GPT-5 Codex uses 229.7x more bold

Claude 3 Opus
GPT-5 Codex
54%Vocabulary64%
14wSentence Length17w
0.48Hedging0.38
0.0Bold2.3
3.0Lists3.5
0.00Emoji0.15
0.00Headings0.49
0.06Transitions0.05
Based on 3 + 13 text responses
vs

Ask them anything yourself

Claude 3 OpusGPT-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
FAQ

Common questions