Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Gemini 3.5 Flash
87
GPT-5.5 Pro
100
Verified leaderboard positions: Gemini 3.5 Flash #6 · GPT-5.5 Pro unranked
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Gemini 3.5 Flash only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
Agentic
+12.9 difference
Knowledge
+0.8 difference
Gemini 3.5 Flash
GPT-5.5 Pro
$1.5 / $9
$30 / $180
284.2 t/s
N/A
18.55s
N/A
1M
1M
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Gemini 3.5 Flash only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
GPT-5.5 Pro is clearly ahead on the provisional aggregate, 100 to 87. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.5 Pro's sharpest advantage is in agentic, where it averages 90.1 against 77.2. The single biggest benchmark swing on the page is HLE, 40.2% to 57.2%. Gemini 3.5 Flash does hit back in knowledge, so the answer changes if that is the part of the workload you care about most.
GPT-5.5 Pro is also the more expensive model on tokens at $30.00 input / $180.00 output per 1M tokens, versus $1.50 input / $9.00 output per 1M tokens for Gemini 3.5 Flash. That is roughly 20.0x on output cost alone.
GPT-5.5 Pro is ahead on BenchLM's provisional leaderboard, 100 to 87. The biggest single separator in this matchup is HLE, where the scores are 40.2% and 57.2%.
Gemini 3.5 Flash has the edge for knowledge tasks in this comparison, averaging 58 versus 57.2. Inside this category, HLE is the benchmark that creates the most daylight between them.
GPT-5.5 Pro has the edge for agentic tasks in this comparison, averaging 90.1 versus 77.2. Gemini 3.5 Flash stays close enough that the answer can still flip depending on your workload.
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