BlackRock’s IBIT spot Bitcoin exchange-traded fund crossed 300,000 BTC +1.06% ($21 billion) in assets under management on Thursday, five months after trading began on Jan. 11.

BlackRock’s Bitcoin ETF has now accumulated 302,534 BTC, according to its fund page, with around 4,920 BTC in net inflows yesterday taking it over the milestone.

IBIT overtook Grayscale’s GBTC in terms of AUM last week, catching the product that had a head start over the other spot Bitcoin ETFs in assets. GBTC originally operated as a private placement fund before transitioning to public trading on the OTC market in 2015 and its ultimate conversion to an ETF in January.

GBTC charges a much higher fee than its competitors — 1.5% compared to the current 0.25% fee for BlackRock’s IBIT, for example — with its post-conversion bitcoin holdings falling approximately 54% from around 619,220 BTC to 285,651 BTC, according to the fund’s disclosures as of Thursday.

However, given the concurrent rise in bitcoin’s price since the spot ETFs launched, GBTC’s assets under management in U.S. dollar terms have fallen less — down 30% from a value of $28.7 billion on Jan. 11 to $20 billion at current prices.

The combined assets held by all the U.S. spot bitcoin ETFs are now at nearly 883,000 BTC ($63 billion), according to CoinGlass data — 4.2% of bitcoin’s total 21 million supply.

US spot Bitcoin ETFs hit record net inflow streak

The U.S. spot Bitcoin ETFs reached a record 18-day net inflow streak on Thursday, adding a further $217.7 million to the funds, during a week in which they have generated nearly $1.7 billion in net inflows so far. 

BlackRock’s IBIT led yesterday's net inflows, bringing in $349.9 million, with Grayscale’s GBTC witnessing $37.6 million in net outflows.

While daily inflows into the spot Bitcoin ETFs have picked up back toward record levels this week, volume remains significantly below the March 12 $9.9 billion peak, generating $1.4 billion in trading yesterday.