Claude 3 Opus vs GPT-5.1-Codex

Compare Claude 3 Opus by Anthropic against GPT-5.1-Codex by OpenAI, context windows of 200K vs 400K, tested across 12 shared challenges. Updated April 2026.

Which is better, Claude 3 Opus or GPT-5.1-Codex?

Claude 3 Opus and GPT-5.1-Codex are both competitive models. Claude 3 Opus costs $15/M input tokens vs $1.25/M for GPT-5.1-Codex. Context windows: 200K vs 400K tokens. Compare their real outputs side by side below.

Key Differences Between Claude 3 Opus and GPT-5.1-Codex

Claude 3 Opus is made by anthropic while GPT-5.1-Codex is from openai. Claude 3 Opus has a 200K token context window compared to GPT-5.1-Codex's 400K. On pricing, Claude 3 Opus costs $15/M input tokens vs $1.25/M for GPT-5.1-Codex.

Our Verdict
GPT-5.1-Codex
GPT-5.1-Codex
Claude 3 Opus
Claude 3 OpusRunner-up

No community votes yet. On paper, GPT-5.1-Codex has the edge — newer, bigger context window.

GPT-5.1-Codex is 7.5x cheaper per token — worth considering if cost matters.

Too close to call
Writing DNA

Style Comparison

Similarity
97%

GPT-5.1-Codex uses 343.9x more bold

Claude 3 Opus
GPT-5.1-Codex
54%Vocabulary70%
14wSentence Length17w
0.48Hedging0.39
0.0Bold3.4
3.0Lists3.5
0.00Emoji0.00
0.00Headings0.50
0.06Transitions0.38
Based on 3 + 14 text responses
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Claude 3 OpusGPT-5.1-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
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