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Bubble forming? No way, says Y Combinator prez

Many experts, analysts and venture capitalists have largely exaggerated the possibility that a valuation bubble exists among today's start-ups, Y Combinator's President Sam Altman said Wednesday.

"I think people talk about a bubble because it's an easy way to get on TV, … but I think these companies are doing incredible work, and by and large the valuations are reasonable," Altman said in an interview with CNBC's "Squawk Alley."

"I don't think most VCs believe we're in a bubble. ... If they do, then they shouldn't invest in start-ups," said Altman, whose company provides seed money to start-ups like Airbnb, Twitch and Disqus.

Several start-ups now have multibillion-dollar valuations, including Uber, valued at over $40 billion, and Snapchat, which was valued at about $10 billion last August.

Altman said some of the venture capitalists who have made the most noise regarding these high valuations are also the ones who are pumping the most money into them. "The VCs that are investing the most money ever in start-ups, at least in the last 10 years, are the ones that are saying there's a bubble."

He also said these venture capitalists are exaggerating the possibility of a bubble because of their lack of control over the companies. "I think what's going on is that VCs have sort of less and less of the power in this sort of company dynamic, and so, people are like, 'Oh, [start-ups] are hugely overinflated.'"

Read More Pessimism reigns as investors weigh valuations

Another reason start-up valuations are this high is because of the a long-standing low interest rate environment, Altman said.

"Yeah, valuations are high, and interest rates are zero, so that's to be expected, but I don't think valuations have become wildly disconnected from [actual values]."