“My median for the longest 50% time horizon reported as of Dec 31, 2026 is 24 hours (20th percentile 15 hours, 80th percentile is that it's too long for METR to accurately bound in practice but probably around 40 hours in 'reality').”

Baseline was Claude Opus 4.5 at ~5 hours; by March 2026 Cotra wrote that Opus 4.6's estimated ~12-hour horizon made her 24-hour median look 'much too conservative.'