In early internal use, Claude Mythos preview reached unprecedented levels of reliability and alignment, leading to broader use with less frequent human interaction than prior models.

Claude Mythos achieved an 82% score on the terminal bench, an increase from the previous 65%.

Anthropic's Claude Mythos model is a much bigger, more expensive, slower, but more powerful model compared to Opus.

On Humanity's Last Exam, Claude Mythos improved its score from 40% to 56.8%, and to 64.7% when given tools.

Anthropic will not widely release its Claude Mythos Preview model because of its potential to cause harm if misused.

Anthropic has been using the Claude Mythos model internally since February 24th, 2026.