Head-to-head comparison across 4benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Mythos Preview
99
GPT-5.5
89
Verified leaderboard positions: Claude Mythos Preview #1 · GPT-5.5 #2
Pick Claude Mythos Preview if you want the stronger benchmark profile. GPT-5.5 only becomes the better choice if you want the cheaper token bill.
Agentic
+0.6 difference
Coding
+25.2 difference
Knowledge
+8.5 difference
Multimodal
+23.7 difference
Claude Mythos Preview
GPT-5.5
$25 / $125
$5 / $30
N/A
N/A
N/A
N/A
1M
1M
Pick Claude Mythos Preview if you want the stronger benchmark profile. GPT-5.5 only becomes the better choice if you want the cheaper token bill.
Claude Mythos Preview is clearly ahead on the provisional aggregate, 99 to 89. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Claude Mythos Preview's sharpest advantage is in coding, where it averages 83.8 against 58.6. The single biggest benchmark swing on the page is SWE-bench Pro, 77.8% to 58.6%.
Claude Mythos Preview is also the more expensive model on tokens at $25.00 input / $125.00 output per 1M tokens, versus $5.00 input / $30.00 output per 1M tokens for GPT-5.5. That is roughly 4.2x on output cost alone.
Claude Mythos Preview is ahead on BenchLM's provisional leaderboard, 99 to 89. The biggest single separator in this matchup is SWE-bench Pro, where the scores are 77.8% and 58.6%.
Claude Mythos Preview has the edge for knowledge tasks in this comparison, averaging 74.9 versus 66.4. Inside this category, HLE w/o tools is the benchmark that creates the most daylight between them.
Claude Mythos Preview has the edge for coding in this comparison, averaging 83.8 versus 58.6. Inside this category, SWE-bench Pro is the benchmark that creates the most daylight between them.
Claude Mythos Preview has the edge for agentic tasks in this comparison, averaging 82.4 versus 81.8. Inside this category, BrowseComp is the benchmark that creates the most daylight between them.
Claude Mythos Preview has the edge for multimodal and grounded tasks in this comparison, averaging 92.7 versus 69. Inside this category, MMMU-Pro is the benchmark that creates the most daylight between them.
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