GPT-5.1-Codex vs GPT-5.5
Compare GPT-5.1-Codex and GPT-5.5, both from OpenAI, context windows of 400K vs 1.1M, tested across 52 shared challenges.
Our Verdict
GPT-5.5
GPT-5.1-CodexRunner-up
No community votes yet. On paper, GPT-5.5 has the edge — newer, bigger context window.
GPT-5.1-Codex is 3.0x cheaper per token — worth considering if cost matters.
Too close to call
API pricing
Cost per 1M tokens
GPT-5.1-Codex
Input
$1.25
4.0× cheaper
Output
$10.00
3.0× cheaper
GPT-5.5
Input
$5.00
Output
$30.00
GPT-5.1-Codex is cheaper on both — 4.0× input, 3.0× output
Writing DNA
Style Comparison
Similarity
48%
GPT-5.1-Codex uses 11.2x more transitions
GPT-5.1-Codex
GPT-5.5
70%Vocabulary58%
17wSentence Length18w
0.39Hedging0.74
3.4Bold2.9
3.5Lists5.1
0.00Emoji0.00
0.50Headings1.68
0.38Transitions0.03
Based on 14 + 26 text responses
Research
What we learned reading every model
FAQ
