Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Gemini 3.5 Flash
81
GPT-5.3 Codex
83
Verified leaderboard positions: Gemini 3.5 Flash #9 · GPT-5.3 Codex unranked
Pick GPT-5.3 Codex if you want the stronger benchmark profile. Gemini 3.5 Flash only becomes the better choice if agentic is the priority or you want the cheaper token bill.
Agentic
+5.7 difference
Coding
+8.6 difference
Gemini 3.5 Flash
GPT-5.3 Codex
$1.5 / $9
$1.75 / $14
284.2 t/s
79 t/s
18.55s
88.26s
1M
400K
Pick GPT-5.3 Codex if you want the stronger benchmark profile. Gemini 3.5 Flash only becomes the better choice if agentic is the priority or you want the cheaper token bill.
GPT-5.3 Codex has the cleaner provisional overall profile here, landing at 83 versus 81. It is a real lead, but still close enough that category-level strengths matter more than the headline number.
GPT-5.3 Codex's sharpest advantage is in coding, where it averages 63.1 against 54.5. The single biggest benchmark swing on the page is OSWorld-Verified, 78.4% to 64.7%. Gemini 3.5 Flash does hit back in agentic, so the answer changes if that is the part of the workload you care about most.
GPT-5.3 Codex is also the more expensive model on tokens at $1.75 input / $14.00 output per 1M tokens, versus $1.50 input / $9.00 output per 1M tokens for Gemini 3.5 Flash. Gemini 3.5 Flash gives you the larger context window at 1M, compared with 400K for GPT-5.3 Codex.
GPT-5.3 Codex is ahead on BenchLM's provisional leaderboard, 83 to 81. The biggest single separator in this matchup is OSWorld-Verified, where the scores are 78.4% and 64.7%.
GPT-5.3 Codex has the edge for coding in this comparison, averaging 63.1 versus 54.5. Inside this category, Vibe Code Bench is the benchmark that creates the most daylight between them.
Gemini 3.5 Flash has the edge for agentic tasks in this comparison, averaging 77.2 versus 71.5. Inside this category, OSWorld-Verified is the benchmark that creates the most daylight between them.
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