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Claude Opus 4.5 vs GPT OSS 120B

Compare Claude Opus 4.5 by Anthropic against GPT OSS 120B by OpenAI, tested across 49 shared challenges. Updated April 2026.

Which is better, Claude Opus 4.5 or GPT OSS 120B?

Claude Opus 4.5 and GPT OSS 120B are both competitive models. Compare their real outputs side by side below.

Key Differences Between Claude Opus 4.5 and GPT OSS 120B

Claude Opus 4.5 is made by anthropic while GPT OSS 120B is from openai.

Our Verdict
Claude Opus 4.5
Claude Opus 4.5
GPT OSS 120B
GPT OSS 120B

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
97%

GPT OSS 120B uses 3.2x more transitions

Claude Opus 4.5
GPT OSS 120B
64%Vocabulary52%
55wSentence Length19w
0.86Hedging0.28
5.8Bold7.4
4.5Lists1.8
0.15Emoji0.15
1.59Headings0.73
0.05Transitions0.17
Based on 24 + 21 text responses
vs

Ask them anything yourself

Claude Opus 4.5GPT OSS 120B

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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