Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Mythos 5
99
GPT-5.3 Codex
86
Verified leaderboard positions: Claude Mythos 5 #1 · GPT-5.3 Codex unranked
Pick Claude Mythos 5 if you want the stronger benchmark profile. GPT-5.3 Codex only becomes the better choice if you want the cheaper token bill.
Agentic
+15.5 difference
Coding
+22.8 difference
Claude Mythos 5
GPT-5.3 Codex
$10 / $50
$1.75 / $14
N/A
79 t/s
N/A
88.26s
1M+
400K
Pick Claude Mythos 5 if you want the stronger benchmark profile. GPT-5.3 Codex only becomes the better choice if you want the cheaper token bill.
Claude Mythos 5 is clearly ahead on the provisional aggregate, 99 to 86. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Claude Mythos 5's sharpest advantage is in coding, where it averages 85.9 against 63.1. The single biggest benchmark swing on the page is SWE-bench Pro, 80.3% to 56.8%.
Claude Mythos 5 is also the more expensive model on tokens at $10.00 input / $50.00 output per 1M tokens, versus $1.75 input / $14.00 output per 1M tokens for GPT-5.3 Codex. That is roughly 3.6x on output cost alone. Claude Mythos 5 gives you the larger context window at 1M+, compared with 400K for GPT-5.3 Codex.
Claude Mythos 5 is ahead on BenchLM's provisional leaderboard, 99 to 86. The biggest single separator in this matchup is SWE-bench Pro, where the scores are 80.3% and 56.8%.
Claude Mythos 5 has the edge for coding in this comparison, averaging 85.9 versus 63.1. Inside this category, SWE-bench Pro is the benchmark that creates the most daylight between them.
Claude Mythos 5 has the edge for agentic tasks in this comparison, averaging 87 versus 71.5. Inside this category, GDPval-AA is the benchmark that creates the most daylight between them.
For engineers, researchers, and the plain curious — a weekly brief on new models, ranking shifts, and pricing changes.
Free. No spam. Unsubscribe anytime.