GBTC is a bitcoin ETN (exchange traded note). It trades on the NASDAQ OTC. It is fairly liquid with average daily dollar volume around $57 million.
Months ago, it sometimes lagged or overshot (it soared from $110 to $565 from April to May this year vs. bitcoin's price rise from about $1000 to nearly $3000), but now tracks the price of bitcoin much better.
Meanwhile, Canada is about to launch a bitcoin ETF: https://bitcoinist.com/first-bitcoin-etf-launch-canada/
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