Boston-based Bracebridge Capital has emerged as a major player in the Bitcoin ETF landscape, owning $433 million in Bitcoin through ETFs, with significant holdings in ARK, BlackRock, and Grayscale. Switzerland's UBS and Canada's Bank of Montreal have also disclosed owning Bitcoin ETFs, with UBS holding BlackRock's ETF and Bank of Montreal having multiple Bitcoin ETF holdings. Additionally, prominent hedge fund Millennium Management has made a substantial investment of $2 billion in Bitcoin ETFs, representing 3% of their $64 billion fund.