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Claude Opus 4.5 vs OpenAI o4-mini

Compare Claude Opus 4.5 by Anthropic against OpenAI o4-mini by OpenAI, tested across 35 shared challenges. Updated April 2026.

Which is better, Claude Opus 4.5 or OpenAI o4-mini?

Claude Opus 4.5 and OpenAI o4-mini are both competitive models. Compare their real outputs side by side below.

Key Differences Between Claude Opus 4.5 and OpenAI o4-mini

Claude Opus 4.5 is made by anthropic while OpenAI o4-mini is from openai.

Our Verdict
Claude Opus 4.5
Claude Opus 4.5
OpenAI o4-mini
OpenAI o4-miniRunner-up

No community votes yet. On paper, Claude Opus 4.5 has the edge — bigger model tier, newer.

Too close to call
Writing DNA

Style Comparison

Similarity
84%

Claude Opus 4.5 uses 580.0x more bold

Claude Opus 4.5
OpenAI o4-mini
64%Vocabulary73%
55wSentence Length15w
0.86Hedging0.18
5.8Bold0.0
4.5Lists2.1
0.15Emoji0.00
1.59Headings0.00
0.05Transitions0.02
Based on 24 + 10 text responses
vs

Ask them anything yourself

Claude Opus 4.5OpenAI o4-mini

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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