On the latest episode of The Ezra Klein Show, Bill Gates elaborated a bit on his views about AI timelines (starting around 24:40):

Klein: I know you take… the risk of creating artificial intelligence that… ends up turning against us pretty seriously. I’m curious where you think we are in terms of creating an artificial intelligence…

Gates: Well, with robotics you have to think of three different milestones.

One is… not-highly-trained labor substitution. Driving, security guard, warehouse work, waiter, maid — things that are largely visual and physical manipulation… [for] that threshold I don’t think you’d get much disagreement that over the next 15 years that the robotic equivalents in terms of cost [and] reliability will become a substitute to those activities…

Then there’s the point at which what we think of as intelligent activities, like writing contracts or doing diagnosis or writing software code, when will the computer start to… have the capacity to work in those areas? There you’d get more disagreement… some would say 30 years, I’d be there. Some would say 60 years. Some might not even see that [happening].

Then there’s a third threshold where the intelligence involved is dramatically better than humanity as a whole, what Bostrom called a “superintelligence.” There you’re gonna get a huge range of views including people who say it won’t ever happen. Ray Kurzweil says it will happen at midnight on July 13, 2045 or something like that and that it’ll all be good. Then you have other people who say it can never happen. Then… there’s a group that I’m more among where you say… we’re not able to predict it, but it’s something that should start thinking about. We shouldn’t restrict activities or slow things down… [but] the potential that that exists even in a 50-year timeframe [means] it’s something to be taken seriously.

But those are different thresholds, and the responses are different.

See Gates’ previous comments on AI timelines and AI risk, here.

UPDATE 07/01/2016: In this video, Gates says that achieving “human-level” AI will take “at least 5 times as long as what Ray Kurzweil says.”