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Amazon CEO Jeff Bezos is very bullish on his company's artificial intelligence push. So bullish, in fact, that Amazon has invested four years of research into its key project in AI — and stacked that project with a sizable staff.

Bezos said at the Code Conference that the team on Alexa, Amazon's smart voice-assistant software, and Echo, its flagship device, is now more than 1,000 employees.

"We've been working behind the scenes for the last four years," he said about Echo and Alexa. "It's just the tip of the iceberg."

Other tech giants are moving into the space. Google recently previewed its coming Echo rival. Apple reportedly has one in the works.

Bezos dodged direct questions about competitors. He said voice interfaces won't replace phones altogether, but admitted that this field of AI is only getting bigger — and noted one of Amazon's edges over the competition.

"There will be huge advances," he said. "Bigger companies like Amazon have an advantage because you need a lot of data to do extraordinary things."

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Correction: An earlier version of this story incorrectly stated that this was the first time Bezos discussed the number of employees working on this initiative. He discussed it recently in an interview with the Washington Post, which he owns.