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  5. GPT-5.1 Codex MaxvsOpenAI o3
Updated Dec 2025

GPT-5.1 Codex MaxvsOpenAI o3

GPT-5.1 Codex Max is the newer model, released after OpenAI o3.

GPT-5.1 Codex Max and OpenAI o3 compared across 53 shared prompts
SpecGPT-5.1 Codex MaxOpenAI o3
Input price—$10/M tokens
Output price—$40/M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedDec 2025Apr 2025
SWE-bench Verified77.9%69.1%
Our Verdict
GPT-5.1 Codex Max
GPT-5.1 Codex Max
OpenAI o3
OpenAI o3

Not enough votes to call it. On the specs, nothing separates them.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.1 Codex Max
Input
—
Output
—
OpenAI o3
Input
$10.00
Output
$40.00
Where to run it

2 hosts

GPT-5.1 Codex Max1 host
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% up
OpenAI o31 host
HostInOutContextUptime
OpenAI$2.00 in·$8.00 out·200k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 13 Sep 2026.

Writing DNA

Style Comparison

Similarity
73%

GPT-5.1 Codex Max uses 3.8x more bold

GPT-5.1 Codex Max
OpenAI o3
60%Vocabulary70%
16wSentence Length14w
0.36Hedging0.27
2.3Bold0.6
4.2Lists2.8
0.00Emoji0.00
0.12Headings0.32
0.03Transitions0.10
Based on 13 + 19 text responses
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