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Claude Opus 4.5 vs GPT-5 Nano

Compare Claude Opus 4.5 by Anthropic against GPT-5 Nano by OpenAI, tested across 46 shared challenges. Updated April 2026.

Which is better, Claude Opus 4.5 or GPT-5 Nano?

Claude Opus 4.5 and GPT-5 Nano are both competitive models. Compare their real outputs side by side below.

Key Differences Between Claude Opus 4.5 and GPT-5 Nano

Claude Opus 4.5 is made by anthropic while GPT-5 Nano is from openai.

Our Verdict
Claude Opus 4.5
Claude Opus 4.5
GPT-5 Nano
GPT-5 NanoRunner-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
100%

Claude Opus 4.5 uses 580.0x more bold

Claude Opus 4.5
GPT-5 Nano
64%Vocabulary59%
55wSentence Length25w
0.86Hedging0.23
5.8Bold0.0
4.5Lists4.2
0.15Emoji0.00
1.59Headings0.00
0.05Transitions0.01
Based on 24 + 14 text responses
vs

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Claude Opus 4.5GPT-5 Nano

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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