benchlm.ai

GPT-5.1-Codex-Max vs GPT-OSS 20B

Side-by-side benchmark comparison across knowledge, coding, math, and reasoning.

Quick Verdict

GPT-5.1-Codex-Max wins overall with a score of 77 vs 22 (55 point difference).GPT-5.1-Codex-Max wins 4 out of 4 categories.

GPT-5.1-Codex-Max

CreatorOpenAI
TypeProprietary
Context400K
Score77

GPT-OSS 20B

CreatorOpenAI
TypeOpen Weight
Context128K
Score22

Knowledge

GPT-5.1-Codex-Max

GPT-5.1-Codex-Max

95

GPT-OSS 20B

28.8

98
MMLU
31
96
GPQA
30
94
SuperGPQA
28
92
OpenBookQA
26

Coding

GPT-5.1-Codex-Max

GPT-5.1-Codex-Max

94

GPT-OSS 20B

23

94
HumanEval
23

Mathematics

GPT-5.1-Codex-Max

GPT-5.1-Codex-Max

97.1

GPT-OSS 20B

30

99
AIME 2023
31
99
AIME 2024
33
98
AIME 2025
32
95
HMMT Feb 2023
27
97
HMMT Feb 2024
29
96
HMMT Feb 2025
28
96
BRUMO 2025
30

Reasoning

GPT-5.1-Codex-Max

GPT-5.1-Codex-Max

93

GPT-OSS 20B

28

94
SimpleQA
29
92
MuSR
27

Frequently Asked Questions

Which is better, GPT-5.1-Codex-Max or GPT-OSS 20B?

GPT-5.1-Codex-Max scores higher overall with 77 vs 22, a difference of 55 points across all benchmarks.

Which is better for knowledge tasks, GPT-5.1-Codex-Max or GPT-OSS 20B?

GPT-5.1-Codex-Max leads in knowledge tasks with an average score of 95 vs 28.8.

Which is better for coding, GPT-5.1-Codex-Max or GPT-OSS 20B?

GPT-5.1-Codex-Max leads in coding with an average score of 94 vs 23.

Which is better for math, GPT-5.1-Codex-Max or GPT-OSS 20B?

GPT-5.1-Codex-Max leads in math with an average score of 97.1 vs 30.

Which is better for reasoning, GPT-5.1-Codex-Max or GPT-OSS 20B?

GPT-5.1-Codex-Max leads in reasoning with an average score of 93 vs 28.

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