Claude Sonnet 4.5vsGPT-5.1-Codex
GPT-5.1-Codex is cheaper than Claude Sonnet 4.5 at $1.25/M vs $3/M input tokens.
| Spec | Claude Sonnet 4.5 | GPT-5.1-Codex |
|---|---|---|
| Input price | $3/M tokens | $1.25/M tokens |
| Output price | $15/M tokens | $10/M tokens |
| Context window | 200K tokens | 400K tokens |
| Released | Sep 2025 | Nov 2025 |
| SWE-bench Verified | 77.2% | 73.7% |
Our Verdict
GPT-5.1-Codex
Claude Sonnet 4.5Runner-up
Not enough votes to call it. On the specs, GPT-5.1-Codex has the edge: bigger model tier, newer, bigger context window.
Pick Claude Sonnet 4.5 for Reasoning. Pick GPT-5.1-Codex for Web Design.
Slight edge
API pricing
Cost per 1M tokens
Claude Sonnet 4.5
Input
$3.00
Output
$15.00
GPT-5.1-Codex
Input
$1.25
2.4× cheaper
Output
$10.00
1.5× cheaper
GPT-5.1-Codex is cheaper on both — 2.4× input, 1.5× output
Writing DNA
Style Comparison
Similarity
45%
Claude Sonnet 4.5 uses 45.2x more emoji
Claude Sonnet 4.5
GPT-5.1-Codex
64%Vocabulary70%
94wSentence Length17w
0.48Hedging0.39
4.9Bold3.4
8.0Lists3.5
0.45Emoji0.00
1.91Headings0.50
0.07Transitions0.38
Based on 20 + 14 text responses
Research
What we learned reading every model
FAQ
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