Banks have suddenly cottoned on to the power of the blockchain technology beneath Bitcoin. Inside their own treasuries and innovation labs, and increasingly in collaboration, banks are testing uses for rebranded distributed ledgers to replace their costly, proprietary systems. Enthusiasts see banks creating a new fabric for payments transfer and financial markets, an internet of money. Doubters sense it’s all hype. Big challenges remain, but markets from private equity and syndicated loans to corporate bonds and derivatives may go on private blockchains within months.