Investors in bitcoin and Ethereum have the new IRS chief’s attention.

“Crypto is no longer cash,” Charles Rettig, who was sworn in as commissioner last month, said at an American Institute of CPAs event Nov. 13. “It is information data currency that the IRS has and will have more information about than you could ever imagine.”

Rettig identified tax compliance for virtual currency holders as one of several areas where he would like to see better return preparation...