(Reuters) -A handful of hedge funds, including Millennium Management LLC, and other asset managers are among the institutions that acquired stakes in the recently launched U.S. exchange-traded funds (ETFs) tied to the price of bitcoin in the first quarter, according to recent regulatory filings.

New York-based Millenium revealed it had $2 billion invested in several of the new ETFs as of March 31. That included positions in BlackRock's ( BLK ) iShares Bitcoin Trust ( IBIT ), the Grayscale Bitcoin Trust ( GBTC ), and funds launched by issuers such as Bitwise Investments and ARK Investment Management.

Other purchasers included Boston-based hedge fund manager Bracebridge Capital, which owned $262 million of shares in the ARK 21Shares Bitcoin ETF as of the end of the first quarter and $81 million in the BlackRock ( BLK ) product.

Bracebridge, which did not return calls seeking comment, has among its clients a group of institutional investors such as the endowments of Yale University and Princeton University.

A filing from the state of Wisconsin's investment board, which manages $156 billion in assets for the Wisconsin Retirement System, disclosed purchases of BlackRock's ( BLK ) iShares Bitcoin Trust ( IBIT ) worth more than $99 million as of the end of March. It also disclosed holding of more than $63 million in shares in the Grayscale Bitcoin Trust ( GBTC ).

The State of Wisconsin Investment Board declined to comment.

Other hedge funds with positions in the bitcoin ETFs included some that had already invested in bitcoin before the U.S. Securities and Exchange Commission finally approved the spot bitcoin ETFs in January.

New York-based Hunting Hill Global Capital said it owned $29.1 million in the Fidelity Wise Origin Bitcoin ETF and $21.3 million in the Grayscale Bitcoin Trust ( GBTC ).

Adam Guren, founder and CEO of Hunting Hill, said the firm had been investing in Grayscale's bitcoin trust for a year or more as bitcoin's price and the value of its stake increased ahead of the ETF approval.

Investors have poured some $29 billion into the bitcoin ETFs since January, Morningstar Direct data showed.

The filings appear to confirm that while a handful of hedge funds have taken large positions, retail investors - including investment advisors - remain the largest category of purchasers by number. Hightower Advisors, one of the largest advisory firms in the country, disclosed holdings of about $68 million in the bitcoin ETFs, but declined to comment on portfolio decisions.

The quarterly disclosures, known as 13-F filings, are made to the Securities and Exchange Commission around 45 days after the end of each quarter and may not reflect current positions.

Matt Hougan, chief investment officer of Bitwise, noted in a memo to clients posted on the social media platform X that he expected that by the time all the filings are processed, they will show that as many as 700 institutions own $5 billion or more in the new ETFs. Until these filings appeared, it has been difficult to determine which investors have been behind the buying in the products, which has greatly exceeded even the most bullish estimates and helped drive the price of bitcoin itself to new highs this year.