Bitcoin rose as much as 4% on Thursday to top $37,000 and has more than quadrupled in the past year, according to a composite of prices compiled by Bloomberg. It accounts for about two-thirds of cryptocurrency market value, followed by Ether on about 14%. Ether is up 62% so far this year.

Digital coins are jumping in a world awash with fiscal and monetary stimulus, even as some commentators fear an inevitable bust and others question the basic integrity of crypto markets. Proponents of Bitcoin argue it offers a hedge against dollar weakness and the risk of faster inflation, a bit like gold, while critics decry the intellectual soundness of comparing the two assets.

Active Bitcoin accounts are nearing their all-time high levels of late 2017, according to researcher Flipside Crypto — possibly a sign that some holders are planning to sell. Fewer than 2% of accounts hold 95% of Bitcoin supply, so a few big trades can impact prices. The last big Bitcoin boom began imploding in late 2017.

Some traders pointed to JPMorgan Chase & Co.’s long-term Bitcoin price forecast of $146,000 as possibly fueling the rally. Others said sentiment was boosted by a U.S. regulatory update that allows a class of less volatile coins to be used by banks for payments.