benchlm.ai

GPT-5.3 Codex vs GPT-OSS 120B

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

Quick Verdict

GPT-5.3 Codex wins overall with a score of 85 vs 42 (43 point difference).GPT-5.3 Codex wins 4 out of 4 categories.

GPT-5.3 Codex

CreatorOpenAI
TypeProprietary
Context400K
Score85

GPT-OSS 120B

CreatorOpenAI
TypeOpen Weight
Context128K
Score42

Knowledge

GPT-5.3 Codex

GPT-5.3 Codex

96

GPT-OSS 120B

48.8

99
MMLU
51
97
GPQA
50
95
SuperGPQA
48
93
OpenBookQA
46

Coding

GPT-5.3 Codex

GPT-5.3 Codex

95

GPT-OSS 120B

43

95
HumanEval
43

Mathematics

GPT-5.3 Codex

GPT-5.3 Codex

97.1

GPT-OSS 120B

50

99
AIME 2023
51
99
AIME 2024
53
98
AIME 2025
52
95
HMMT Feb 2023
47
97
HMMT Feb 2024
49
96
HMMT Feb 2025
48
96
BRUMO 2025
50

Reasoning

GPT-5.3 Codex

GPT-5.3 Codex

94

GPT-OSS 120B

48

95
SimpleQA
49
93
MuSR
47

Frequently Asked Questions

Which is better, GPT-5.3 Codex or GPT-OSS 120B?

GPT-5.3 Codex scores higher overall with 85 vs 42, a difference of 43 points across all benchmarks.

Which is better for knowledge tasks, GPT-5.3 Codex or GPT-OSS 120B?

GPT-5.3 Codex leads in knowledge tasks with an average score of 96 vs 48.8.

Which is better for coding, GPT-5.3 Codex or GPT-OSS 120B?

GPT-5.3 Codex leads in coding with an average score of 95 vs 43.

Which is better for math, GPT-5.3 Codex or GPT-OSS 120B?

GPT-5.3 Codex leads in math with an average score of 97.1 vs 50.

Which is better for reasoning, GPT-5.3 Codex or GPT-OSS 120B?

GPT-5.3 Codex leads in reasoning with an average score of 94 vs 48.

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