Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Mythos Preview
99
GPT-5.5 Pro
100
Verified leaderboard positions: Claude Mythos Preview #1 · GPT-5.5 Pro unranked
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Claude Mythos Preview only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
Agentic
+7.7 difference
Knowledge
+17.7 difference
Claude Mythos Preview
GPT-5.5 Pro
$25 / $125
$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 Mythos Preview only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
GPT-5.5 Pro finishes one point ahead on BenchLM's provisional leaderboard, 100 to 99. That is enough to call, but not enough to treat as a blowout. This matchup comes down to a few meaningful edges rather than one model dominating the board.
GPT-5.5 Pro's sharpest advantage is in agentic, where it averages 90.1 against 82.4. The single biggest benchmark swing on the page is HLE, 64.7% to 57.2%. Claude Mythos Preview 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 $25.00 input / $125.00 output per 1M tokens for Claude Mythos Preview.
GPT-5.5 Pro is ahead on BenchLM's provisional leaderboard, 100 to 99. The biggest single separator in this matchup is HLE, where the scores are 64.7% and 57.2%.
Claude Mythos Preview has the edge for knowledge tasks in this comparison, averaging 74.9 versus 57.2. Inside this category, HLE w/o tools 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 82.4. Inside this category, BrowseComp is the benchmark that creates the most daylight between them.
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