PayPal cofounder Max Levchin believes in blockchain technology, but isn’t quite so sure about bitcoin.

“It’s a brilliant mathematical idea, fantastic technology, interesting commodity to speculate on,” he told CNBC on the red carpet of the Breakthrough Awards on Sunday. “TBD on whether it’s a currency or just a way to make money fast. I invest in things that I have a strong, long term point of view on and bitcoin I’m still trying to figure out.”

Investors are certainly making money right now. The Winklevoss twins, Cameron and Tyler, just became the first bitcoin billionaires. Since the brothers first invested in bitcoin, the cryptocurrency’s value has increased over 9,000 percent.

While bitcoin is a specific cryptocurrency, blockchain is the technology that underlies it. There is an increasingly large number of other blockchain-based currencies, including ethereum and litecoin. Generally, benefits of blockchain are that it allows for fast, secure, and anonymous financial transfers.

“I think a form of a blockchain technology, bitcoin or otherwise will be essential and will not go away,” Levchin continued. “Not only that, it will continue advancing and being used in many different industries from financial technology to medicine. But it’s not clear to me whether Bitcoin itself is the great long-term investment.”