Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
GPT-5.1-Codex-Max is clearly ahead on the aggregate, 84 to 58. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.1-Codex-Max's sharpest advantage is in coding, where it averages 75.5 against 33.2. The single biggest benchmark swing on the page is SWE-bench Pro, 84 to 37. Aion-2.0 does hit back in instruction following, so the answer changes if that is the part of the workload you care about most.
GPT-5.1-Codex-Max is also the more expensive model on tokens at $2.00 input / $8.00 output per 1M tokens, versus $0.80 input / $1.60 output per 1M tokens for Aion-2.0. That is roughly 5.0x on output cost alone. GPT-5.1-Codex-Max is the reasoning model in the pair, while Aion-2.0 is not. That usually helps on harder chain-of-thought-heavy tests, but it can also mean more latency and more token spend in real use. GPT-5.1-Codex-Max gives you the larger context window at 400K, compared with 128K for Aion-2.0.
Pick GPT-5.1-Codex-Max if you want the stronger benchmark profile. Aion-2.0 only becomes the better choice if instruction following is the priority or you want the cheaper token bill.
GPT-5.1-Codex-Max
86
Aion-2.0
51.7
GPT-5.1-Codex-Max
75.5
Aion-2.0
33.2
GPT-5.1-Codex-Max
88.2
Aion-2.0
66
GPT-5.1-Codex-Max
92.1
Aion-2.0
70.3
GPT-5.1-Codex-Max
72.6
Aion-2.0
54
GPT-5.1-Codex-Max
91
Aion-2.0
93
GPT-5.1-Codex-Max
87.7
Aion-2.0
78.1
GPT-5.1-Codex-Max
94.9
Aion-2.0
72.1
GPT-5.1-Codex-Max is ahead overall, 84 to 58. The biggest single separator in this matchup is SWE-bench Pro, where the scores are 84 and 37.
GPT-5.1-Codex-Max has the edge for knowledge tasks in this comparison, averaging 72.6 versus 54. Inside this category, HLE is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for coding in this comparison, averaging 75.5 versus 33.2. Inside this category, SWE-bench Pro is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for math in this comparison, averaging 94.9 versus 72.1. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for reasoning in this comparison, averaging 92.1 versus 70.3. Inside this category, MRCRv2 is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for agentic tasks in this comparison, averaging 86 versus 51.7. Inside this category, Terminal-Bench 2.0 is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for multimodal and grounded tasks in this comparison, averaging 88.2 versus 66. Inside this category, MMMU-Pro is the benchmark that creates the most daylight between them.
Aion-2.0 has the edge for instruction following in this comparison, averaging 93 versus 91. Inside this category, IFEval is the benchmark that creates the most daylight between them.
GPT-5.1-Codex-Max has the edge for multilingual tasks in this comparison, averaging 87.7 versus 78.1. Inside this category, MMLU-ProX is the benchmark that creates the most daylight between them.
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