The iShares Bitcoin Trust (IBIT) from BlackRock (BLK) now holds more than $1 billion worth of bitcoin, reaching the milestone just five days after the exchange-traded fund (ETF) began trading on Jan. 11.

IBIT's was a quick sprint to $1 billion, but not the fastest. SPDR Gold Trust (GLD) pulled in $1 billion in just three days back in 2004, according to Bloomberg Senior ETF Analyst Eric Balchunas.

What's Happening With Spot Bitcoin ETFs?

Despite significant outflows, Grayscale Bitcoin Trust (GBTC) still accounts for nearly 90% of the market, according to data shared by Bloomberg Analyst James Seyffart. That dominance is largely thanks to its previous existence as a trust before its conversion to an ETF.

BlackRock's IBIT and the Fidelity Wise Origin Bitcoin Fund (FBTC) have been the most prominent alternatives for investors exiting GBTC following their approval last week by the U.S. Securities and Exchange Commission (SEC).

BlackRock head of US iShares product, Rachel Aguirre told Bloomberg TV that the ETF is seeing flows from many different directions, including from retail investors and self-directed investors.

Who Is Buying Spot Bitcoin ETFs?

According to Vanda Research, retail investor appetite for spot bitcoin ETFs remains "modest." That could also be a function of access to these products. Some brokerages, such as Vanguard, are not offering the spot bitcoin ETFs to their clients while others are offering only a few among those available.

The spot bitcoin ETF market as a whole is expected to grow in the coming years, with some analysts predicting it to grow to $100 billion. In terms of new money coming into the bitcoin (BTCUSD) space, Morgan Creek Capital CEO Mark Yusko has said these new products could open the door for as much as $300 billion to enter the bitcoin market.