The largest holders of the biggest ETF by AUM (Blackrock’s IBIT US) use the ETF as part of a basis trade; they are not long Bitcoin. They short a CME-listed Bitcoin futures contract vs. buying the ETF to earn the spread between the two.[1] This is capital efficient because usually their broker allows them to post the ETF as collateral against their short futures position.
https://open.substack.com/pub/cryptohayes/p/snow-forecast?selection=326b2ab9-ebdf-44c5-a0f0-c74b5d6041ba