Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Sonnet 5
94
GPT-5.5 Pro
100
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Claude Sonnet 5 only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
Agentic
+8.3 difference
Knowledge
+0.2 difference
Claude Sonnet 5
GPT-5.5 Pro
$3 / $15
$30 / $180
N/A
N/A
N/A
N/A
1M
1M
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Claude Sonnet 5 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 94. 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 81.8. The single biggest benchmark swing on the page is BrowseComp, 84.7% to 90.1%. Claude Sonnet 5 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 $3.00 input / $15.00 output per 1M tokens for Claude Sonnet 5. That is roughly 12.0x on output cost alone.
GPT-5.5 Pro is ahead on BenchLM's provisional leaderboard, 100 to 94. The biggest single separator in this matchup is BrowseComp, where the scores are 84.7% and 90.1%.
Claude Sonnet 5 has the edge for knowledge tasks in this comparison, averaging 57.4 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 81.8. Inside this category, BrowseComp is the benchmark that creates the most daylight between them.
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