A mystery whale sold $1.29 billion worth of BlackRock’s iShares Bitcoin Trust through a dark pool on Tuesday, marking one of the largest known block trades tied to the world’s biggest Bitcoin ETF.

The trade involved about 29 million IBIT shares and was flagged by Galaxy Research head Alex Thorn, who described it as the largest IBIT dark pool trade he had seen. The transaction was executed at around 10:30 a.m. ET, according to market reports.

The sale came as US spot Bitcoin ETFs faced another day of heavy redemptions. The 11 funds recorded about $334 million in net outflows on Tuesday, while investors have pulled roughly $2.26 billion from the products over the past two weeks.

BlackRock’s IBIT also recorded a net outflow of about $192 million on Tuesday, according to SoSoValue data. That suggests the dark pool print landed during a broader exit from spot Bitcoin ETF exposure, even though the full $1.29 billion block trade does not automatically mean the seller redeemed shares from the fund.

Dark pool trades are private, off exchange transactions often used by large investors to move size without immediately disrupting the public order book. In this case, buyers appeared to absorb the block, with IBIT’s price remaining relatively stable after the trade, according to Bloomberg ETF analyst Eric Balchunas.

The trade adds to pressure on Bitcoin, which has slipped below $77,000 as ETF outflows accelerate. The latest outflow streak has turned one of Bitcoin’s biggest demand engines into a short term headwind, with investors rotating out of spot ETF exposure after months of institutional accumulation.