GPT 5.1 Codex

Coding-focused GPT-5.1 variant with optimized routing.

Reasoning
Vision

Added Nov 13, 2025

Pricing

Auto routing · per 1M tokens

Input: $1.25
Output: $10.00
Cache read: $0.13

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Specifications

Context window: 400K
Max output: 128K
Avg output (7d): 66 tokens; Longer than 4% of models

Benchmarks

Artificial Analysis

Design Arena

Sourced from Artificial Analysis.

Intelligence Index

23.7

Better than 72% of models compared

Agentic work

T²-Bench Telecom (legacy)

Legacy fallback · Conversational AI agents in dual-control scenarios

83.0%

Better than 73% of models compared

Document reasoning

AA-LCR v1.1

Long context reasoning with updated grading

69.3%

Better than 61% of models compared

Reasoning

HLE

Humanity's Last Exam

25.7%

Better than 73% of models compared

IFBench

Instruction-following benchmark

70.0%

Better than 84% of models compared

CritPt

Research-level physics reasoning

5.7%

Coding

Terminal-Bench Hard (legacy)

Legacy fallback · Agentic coding and terminal use

34.8%

Better than 80% of models compared

LiveCodeBench

Contamination-free coding benchmark

84.9%

Better than 96% of models compared

Math

AIME 2025

American Invitational Mathematics Examination 2025

95.7%

Better than 97% of models compared

Knowledge

MMLU-Pro

Professional and academic subject knowledge

86.0%

Better than 94% of models compared

AA-Omniscience Accuracy

Proportion of correctly answered questions

39.9%

AA-Omniscience Hallucination Rate

Rate of incorrect answers among non-correct responses

77.2%

Legacy benchmarks

GPQA Diamond (legacy)

Graduate-level scientific reasoning

86.0%

Better than 80% of models compared

AA-LCR (unversioned / legacy)

Long context reasoning evaluation