 by METR, for the first Claude 4.5 Opus thinking model to appear on METR's graph.

50% time horizon is a measure of AI autonomy based on the length of tasks that AI can do: roughly, it is the time that humans take to complete tasks that an AI system can successfully do 50% of the time. See 

Measuring AI Ability to Complete Long Tasks"

for the technical definition. Claude 3.7 Sonnet, released in February 2025, was the leading model with a 50% horizon of 59 minutes. 

Left bounds inclusive, right bounds exclusive.