Estimating GBTC price from BTC after-hours activity

Grayscale Bitcoin Trust (GBTC) is the name of a publicly traded OTC investment product listed on the public OTC markets. It’s a way for US investors to take a position in Bitcoin through brokerage and retirement accounts like IRAs. A lot of OG crypto-types scoff at the prospect of purchasing such an asset, since you don’t actually control the BTC or the private keys, but for some this is an attractive option, or an only one. I’ve been personally taking positions in GBTC over the past 3 or so years through my retirement IRA. One of the most underlooked qualities of GBTC through an IRA is that all transactions are tax-free. I can take profits in my IRA at any time without worrying about tax liability, which is not something I can say for my actual crypto holdings.

Two of the downsides of GBTC is that Grayscale takes a two percent management fee. This isn’t a big deal to me because of the expected gains in a bull run. The other is that there is a premium on GBTC over the underlying asset value. Each share of GBTC represents .00096884 Bitcoin, but the GBTC’s price is usually 30-10% higher than the value of the underlying asset.

One of the main differences between the equities and crypto markets is the fact that crypto is 24/7. Often, during times when BTC has made a big price movement, I’ve wondered what the corresponding change in the price of GBTC would be (and in my portfolio!) So, I have written a small Python package to calculate this that I call GBTC Estimator.

I have it setup to get public BTC prices from Gemini (via the excellent CCXT package). Right now it’s using IEX’s daily GBTC data (and required an IEX API key), so it only has access to daily OHLCV (open, high, low, close, volume) data. We take the close price of GBTC, and divide it by the price of BTC at the same time (4PM EST) to come up with the actual BTC per share. This number is then used with the current BTC price to come up with the estimated GBTC value.

This current version is run from the command line and returns the estimated price as well as the difference from the last close in dollars and percentage. I have plans to put this up as a website that updates automatically, but first I think I’m going to do some backtesting to see how accurate this is. I think there may be some arbitrage opportunities to be found here. I’ve already started refactoring and will have more updates to follow.