Task Horizon
The length of tasks a model can complete with a given probability (50% in METR's headline measure), where length is how long the same task takes a human. METR defined it in March 2025.
AI and GrowthTerm 71 / 81
In practice
According to METR's March 2025 measurement, over the past six years this length followed an exponential trend, doubling roughly every seven months. Know the limits: it is measured on multi-step software and reasoning tasks, and the authors themselves note the possibility of substantial model error. The growth reading: give agents short, reversible work first (one email variant, one segment list) and keep long, multi-step work (running a campaign end to end) under human approval (our reading). Order the agent work in your growth roadmap by task length, but do not tie the schedule to a trend line (our reading).