BlackRock’s bitcoin exchange-traded funds (ETFs) have become the firm’s most profitable product line, according to Cristiano Castro, director of business development at BlackRock Brazil.

The figure is notable given that the firm manages over 1,400 ETFs globally and is the world’s largest asset manager with more than $13.4 trillion in assets under management.

Speaking at the Blockchain Conference in São Paulo to local media, Castro called the development “a big surprise” and said that allocations in the firm’s bitcoin ETFs, including the U.S.-based IBIT and Brazil’s IBIT39, had come close to $100 billion.

“When we launched, we were optimistic,” Castro said, “but we didn’t expect this scale.”

The firm’s U.S.-listed spot bitcoin ETF IBIT, launched in January 2024, became the fastest in history to reach $70 billion in assets, doing so in 341 days. That momentum has continued despite recent volatility in bitcoin’s price, with the ETF currently sitting at $70.7 billion in net assets according to SoSoValue data.

Net inflows exceeded $52 billion in its first year, far outpacing all other ETFs launched in the last decade. IBIT also generated an estimated $245 million in annual fees by October 2025.

IBIT’s rapid growth has been fueled by BlackRock’s global distribution network and a wave of institutional interest following U.S. regulatory approval of spot bitcoin ETFs. It now holds over 3% of bitcoin’s total supply, and it was followed by various BTC-linked products from BlackRock, including ETPs overseas.

Castro addressed recent outflows from bitcoin funds, saying that such movement is expected given how retail investors tend to react to price drops. “ETFs are a very liquid and powerful tool. They’re meant for people to manage flows,” he said.

BlackRock itself has been betting on its bitcoin ETF. Its Strategic Income Opportunities Portfolio has recently raised its stake in IBIT by 14%.

CoinDesk has reached out to BlackRock but didn't hear back at the time of writing.