Toby Ord argues hazard rates decline as AI-agent tasks continue

Toby Ord argues hazard rates decline as AI-agent tasks continue

Toby Ord published this argument on February 4, 2026. He says new analysis by Gus Hamilton challenges his earlier constant hazard rate model: estimates using the Weibull distribution put its parameter k below 1 across all models, indicating that hazard rates decline as tasks continue. Ord says this changes estimates on either side of the 50% horizon: longer-task success rates are better, and shorter-task rates worse, than his earlier model suggested. He argues that comparisons between humans and AI agents depend on task length: with the same 50% horizon, humans’ lower k would mean better success on very long tasks but worse success on short ones. He also says k values for AI agents cluster around 0.6, while changes in λ explain improvements in METR timelines. Ord is puzzled that Opus 4.5’s estimated k resembles other AI agents despite its λ resembling humans, and notes that individual-model estimates may be noisy. His main caution is that the Weibull and log-logistic models differ substantially in their tail estimates, including the 99% horizon. He slightly favors Weibull, but says the evidence does not identify which model is right, leaving 99%-reliability horizons deeply uncertain—a threshold he says is necessary for much useful work.

Publication: 30b74863-39b3-73c5-2c13-5459ce5d2c27

attribution — pass: The reading attributes the argument to Toby Ord and the underlying Weibull analysis to Gus Hamilton, matching the source. Ord's own views, such as slightly favoring Weibull and being puzzled about Opus 4.5, are kept distinct from Hamilton's findings.

But some excellent new analysis by Gus Hamilton provides this evidence.

summary — uncertain: The summary is faithful, but central terms are unexplained for a general reader. Only 'AI agent' is defined. The reading never says in plain language what a hazard rate, the 50% horizon or 99% horizon, the Weibull parameter k or λ, or METR are, so the core claim that 'hazard rates decline' is hard to grasp. Smallest repair: plain-language glosses or term-library tooltips for hazard rate, 50%/99% horizon, k and METR. The question is substantive and fair.

It has a second parameter, k, which represents how the hazard rate changes with time (if at all).

date — uncertain: February 4, 2026 matches the UTC day of originalPublished and the page dateline, and no hindsight framing appears. However, editedAfterPublication is true: the page was modified 2026-03-18 per json-ld dateModified. Passages such as the Opus 4.5 'word of warning' cannot be confirmed as part of the original piece rather than a later edit.

February 4, 2026Toby Ord

support — uncertain: Each claim matches the source text: k below 1 for all models; better success beyond the 50% horizon and worse below it; the human-versus-AI comparison; Ord slightly favoring Weibull; and the deep uncertainty about 99% horizons. Because the page was edited after publication (modified 2026-03-18), it is not plain that every cited passage belongs to the original piece, notably the Opus 4.5 remarks. The reading also adds no unsupported benefits or costs.

I'd slightly favour the Weibull, on the grounds that it is more plausible ex ante.

media — pass: No media was selected and no verified candidates were supplied, so nothing was invented or mismatched.