Claude Mythos Preview vs GPT-5.3 Codex — Who Actually Wins? Real Benchmark Data (2026)

head to head

Claude Mythos Preview vs GPT-5.3 Codex

6 shared benchmarks

6

wins

0

ties

0

wins

94.6%

GPQA Diamond

91.5%

56.8%

Humanity's Last Exam

39.9%

79.6%

OSWorld

64.0%

77.8%

SWE-bench Pro

56.8%

93.9%

SWE-bench Verified

80.0%

82.0%

Terminal-Bench 2.0

77.3%