BlackRock, the world's largest asset manager, has submitted an amendment to its Bitcoin spot ETF filing with the U.S. Securities and Exchange Commission (SEC), requesting that Coinbase Custody process customer withdrawals within 12 hours of receiving instructions. The move is seen as a response to concerns raised by investors who have sought on-chain proof of the ETFs' underlying Bitcoin holdings. Coinbase, a leading cryptocurrency exchange and custodian, is responsible for holding the Bitcoin that backs BlackRock's Bitcoin spot ETF (IBIT) and nine other Ethereum spot ETFs. The amendment submitted by BlackRock states that "Coinbase Custody should process cryptocurrency withdrawals from customer custody accounts to publicly disclosed blockchain addresses within 12 hours of receipt of instructions from the customer or its delegate." This request underscores the importance of transparency and liquidity in the burgeoning crypto ETF market. By mandating timely withdrawal processing, BlackRock aims to address investor concerns and enhance the credibility of its crypto ETF offerings. The SEC's decision on BlackRock's amendment will be closely watched by the cryptocurrency industry, as it could set a precedent for other ETF issuers.