Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
GPT-5.3 Codex is clearly ahead on the aggregate, 89 to 56. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.3 Codex's sharpest advantage is in coding, where it averages 87.3 against 27.6. The single biggest benchmark swing on the page is SWE-bench Verified, 85 to 24.
GPT-5.3 Codex is also the more expensive model on tokens at $2.50 input / $10.00 output per 1M tokens, versus $0.08 input / $0.30 output per 1M tokens for Seed 1.6 Flash. That is roughly 33.3x on output cost alone. GPT-5.3 Codex gives you the larger context window at 400K, compared with 256K for Seed 1.6 Flash.
Pick GPT-5.3 Codex if you want the stronger benchmark profile. Seed 1.6 Flash only becomes the better choice if you want the cheaper token bill.
GPT-5.3 Codex
88.1
Seed 1.6 Flash
54.5
GPT-5.3 Codex
87.3
Seed 1.6 Flash
27.6
GPT-5.3 Codex
91.3
Seed 1.6 Flash
73.1
GPT-5.3 Codex
93.7
Seed 1.6 Flash
66.8
GPT-5.3 Codex
80.3
Seed 1.6 Flash
47.3
GPT-5.3 Codex
93
Seed 1.6 Flash
81
GPT-5.3 Codex
92.8
Seed 1.6 Flash
72.8
GPT-5.3 Codex
97.7
Seed 1.6 Flash
67.1
GPT-5.3 Codex is ahead overall, 89 to 56. The biggest single separator in this matchup is SWE-bench Verified, where the scores are 85 and 24.
GPT-5.3 Codex has the edge for knowledge tasks in this comparison, averaging 80.3 versus 47.3. Inside this category, HLE is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for coding in this comparison, averaging 87.3 versus 27.6. Inside this category, SWE-bench Verified is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for math in this comparison, averaging 97.7 versus 67.1. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for reasoning in this comparison, averaging 93.7 versus 66.8. Inside this category, SimpleQA is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for agentic tasks in this comparison, averaging 88.1 versus 54.5. Inside this category, Terminal-Bench 2.0 is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for multimodal and grounded tasks in this comparison, averaging 91.3 versus 73.1. Inside this category, OfficeQA Pro is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for instruction following in this comparison, averaging 93 versus 81. Inside this category, IFEval is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for multilingual tasks in this comparison, averaging 92.8 versus 72.8. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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