"People have asked about the 'dislike' button for many years, and probably hundreds of people have asked about this, and today is a special day because today is the day that I actually get to say we are working on it, and are very close to shipping a test of it," he said.

The CEO said the company has been working on the feature—which would allow users to express emotions other than "like"—for some time because "we don't want to turn Facebook into a forum where people are voting up or down on people's posts."

"That doesn't seem like the kind of community that we want to create: You don't want to go through the process of sharing some moment that was important to you in your day and have someone 'downvote' it," he said, using the lingo of popular online forum Reddit.

Instead, Zuckerberg said, the new feature will allow people to "express empathy" with their Facebook friends, explaining what many users of the social media platform already knew: "If you are sharing something that is sad...then it may not feel comfortable to 'like' that post."

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He added the dislike interaction is "surprisingly complicated" to create, but Facebook thinks it will soon begin testing before a wider roll out.

Questions came in via Facebook posts, comments on a live-stream of the event, and an audience in Menlo Park, California.

The CEO also discussed his company's work with its Oculus virtual reality platform, saying that the experience is "not only going to be things that are in the world, but you'll be able to experience things that aren't even possible to experience in the world"—such as a zero-gravity environment.

Zuckerberg also weighed in on the question of artificial intelligence—a subject which many prominent technologists have warned could one day pose a threat to humanity. He said he was less fearful of the consequences, especially given how many beneficial applications of AI are currently in development (such as autonomous cars).

"I think that it's a little dangerous to be too negative about the prospect of something long term when all signs point to that over the next 10, 20, 30 years—whatever it is—we're going to unlock all this value and help people's lives so much by developing this technology," he said. "So I'm an optimist."