Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Mythos 5
99
GPT-5.5 Pro
100
Verified leaderboard positions: Claude Mythos 5 #1 · GPT-5.5 Pro unranked
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Claude Mythos 5 only becomes the better choice if knowledge is the priority or you want the cheaper token bill.
Agentic
+3.1 difference
Knowledge
+17.4 difference
Claude Mythos 5
GPT-5.5 Pro
$10 / $50
$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 5 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 87. The single biggest benchmark swing on the page is HLE, 64.5% to 57.2%. Claude Mythos 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 $10.00 input / $50.00 output per 1M tokens for Claude Mythos 5. That is roughly 3.6x on output cost alone. Claude Mythos 5 gives you the larger context window at 1M+, compared with 1M for GPT-5.5 Pro.
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 64.5% and 57.2%.
Claude Mythos 5 has the edge for knowledge tasks in this comparison, averaging 74.6 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 87. Inside this category, BrowseComp is the benchmark that creates the most daylight between them.
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