BlackRock's bitcoin exchange-traded funds (ETFs) have quickly become its top revenue source, a surprising development given the firm's extensive portfolio of over 1,400 ETFs and $13.4 trillion in assets under management. The U.S.-listed spot bitcoin ETF, IBIT, launched in January 2024, reached $70 billion in assets within just 341 days, generating an estimated $245 million in annual fees. This rapid growth reflects a surge in institutional interest following U.S. regulatory approval for spot bitcoin ETFs. Currently, IBIT holds more than 3% of the total bitcoin supply. Cristiano Castro, BlackRock’s director of business development in Brazil, highlighted the unexpected success of these bitcoin funds during a talk at the Blockchain Conference in São Paulo. He noted that allocations in the firm’s bitcoin ETFs have approached $100 billion, which he described as a significant surprise. Despite recent market volatility, IBIT has maintained its momentum, with net inflows exceeding $52 billion in its first year, far surpassing any other ETF launched in the past decade. Castro also addressed the typical outflows from bitcoin funds, attributing them to retail investors' reactions to price declines. He emphasized that ETFs offer liquidity and flexibility for managing investment flows. BlackRock has further increased its investment in IBIT through its Strategic Income Opportunities Portfolio, raising its stake by 14%, signaling confidence in the ETF’s continued growth.