BlackRock's IBIT spot Bitcoin exchange-traded fund (ETF) has crossed a significant milestone, surpassing 300,000 BTC (approximately $21 billion) in assets under management (AUM) on Thursday, marking a notable achievement within five months since trading commenced on January 11.

As indicated on its fund page, BlackRock's Bitcoin ETF has accumulated a total of 302,534 BTC, with approximately 4,920 BTC in net inflows recorded yesterday, propelling it over the milestone. This achievement underscores the growing interest and confidence among investors in the cryptocurrency market.

The ascent of BlackRock's IBIT ETF to over 300,000 BTC in AUM comes after it surpassed Grayscale's GBTC in terms of AUM last week, demonstrating its rapid growth and ability to attract investment. Notably, GBTC, which initially operated as a private placement fund before transitioning to public trading on the OTC market in 2015 and later converting to an ETF in January, charges a substantially higher fee compared to its competitors. With GBTC's fee at 1.5% compared to IBIT's current 0.25%, investors are increasingly drawn to lower-cost alternatives such as BlackRock's ETF.

Despite GBTC experiencing a decline in its bitcoin holdings post-conversion, from around 619,220 BTC to 285,651 BTC, its assets under management in U.S. dollar terms have seen a relatively smaller decrease. This decline, from $28.7 billion to $20 billion at current prices, highlights the resilience of GBTC amid market fluctuations.

The combined assets held by all U.S. spot Bitcoin ETFs have now reached nearly 883,000 BTC (equivalent to $63 billion), according to CoinGlass data, representing approximately 4.2% of bitcoin's total 21 million supply. This substantial allocation underscores the growing institutional adoption of bitcoin as an asset class.

On Thursday, the U.S. spot Bitcoin ETFs recorded a record 18-day net inflow streak, with an additional $217.7 million added to the funds. Throughout the week, these ETFs have collectively generated nearly $1.7 billion in net inflows, reflecting sustained investor interest and confidence in the cryptocurrency market.

BlackRock's IBIT ETF led yesterday's net inflows, attracting $349.9 million, while Grayscale's GBTC witnessed $37.6 million in net outflows. Although daily inflows into spot Bitcoin ETFs have increased towards record levels this week, trading volume remains below the peak observed on March 12, which reached $9.9 billion, with $1.4 billion in trading recorded yesterday.