https://www.cnbc.com/2017/12/13/fed-chief-yellen-says-bitcoin-is-a-highly-speculative-asset.html
Yellen has offered little commentary on the surging crytpocurrency during her tenure. She did say back in 2014 that the Fed did not have the authority to regulate bitcoin and reiterated that point on Wednesday.
"The Fed doesn't really play any regulatory role with respect to bitcoin, other than assuring that banking organizations that we do supervise are attentive, that they are appropriately managing any interactions they have with participants in that market, and appropriately monitoring anti-money laundering, bank secrecy act responsibilities that they have," Yellen said.