“From what we can identify, the only reason today to buy or sell bitcoin is to make money, which is the very definition of speculation and the very definition of a bubble,” he said at a news conference in Zurich Thursday. He added that in the history of finance, such speculation has “rarely led to a happy end.” The digital currency got new impetus this week after CME Group Inc., the world’s largest exchange owner, said it plans to introduce bitcoin futures by the end of the year, citing pent-up demand from clients. That pushes bitcoin closer to the mainstream by making it easier to trade without the hassles of owning bitcoin directly.

https://www.bloomberg.com/news/articles/2017-11-02/bitcoin-is-very-definition-of-a-bubble-credit-suisse-ceo-says