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GPT 5.1 Codex Max

Release Date: Dec 4, 2025

Developer OpenAI  🇺🇸
Context Window 400k
Max Output Tokens 128k
Token Costs (in/out) $1.25/10.00
Weights Private
Input Modalities

Accuracy

52.86 %

Avg. Cost (In/Out)

$ 1.25 / $ 10.00

Latency

260 min 25 s

Vals Index
BenchmarksAccuracyRankings
Vibe Code Bench v1.1

0.0%

±3.84
62/96
LiveCodeBench

0.0%

±1.05
48/143
Proprietary BenchmarksAcademic BenchmarksIndustry Partners
Vals
Default Provider : OpenAI
Temperature: Default
Top P: Default
Top K: Default
Max Output Tokens: 128,000
Reasoning Effort: high

Updates

Dec 4, 2025

We’ve evaluated GPT 5.1 Codex Max on our coding benchmarks. It boasts a +9.5% performance boost on VibeCodeBench (#3), +1% performance on SWE-bench Verified (#4), and a slight regression on Terminal-Bench.

This is not the fastest model in the shed. It’s 3x slower on SWE-bench Verified, 10x on VCB. This is a model for when you need the absolute best, not when you need it quickly.

Correlation isn’t causation… …but the more suffixes we tack onto these models, the longer they seem to take. Excited to test 5.25 Codex Max Ultra High Supreme Edition

The model was run with reasoning high and verbosity medium through OpenAI’s API. Results on IOI v1 and LCB will be released soon!