Crypto bank Anchorage Digital said it’ll handle custody for the spot bitcoin product ARK 21Shares Bitcoin ETF.

The only federally chartered crypto bank in the U.S., Anchorage Digital is servicing one of the leading ETFs in a custody space that’s been otherwise dominated by Coinbase Inc.

The first and only U.S. federally chartered crypto bank, Anchorage Digital, is taking on the custody role for a leading issuer of crypto exchange-traded funds (ETFs), 21Shares, the companies said in a Thursday statement.

That custody extends to ARK 21Shares Bitcoin ETF (ARKB), which is behind only BlackRock and Fidelity’s ETFs as the third biggest for inflows, according to a ranking maintained by Farside Investors, and to 21Shares Core Ethereum ETF (CETH). Cathie Wood’s ARK Invest partnered with 21Shares on the bitcoin ETF.

“Anchorage Digital Bank N.A. is pleased to further broaden access to crypto as a custodian selected for 21Shares’ U.S. spot ETF lineup,” said Nathan McCauley, the bank’s co-founder and CEO, in a statement. “Our federal charter — which supersedes state-by-state regulation and positions us as a qualified custodian — makes us a natural choice for ETF custody diversification.”

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The establishment of crypto ETFs was aimed at giving a wider field of investors easier access to regulated products wrapped around the cryptocurrencies that had previously been more difficult to trade. Custody is a hefty responsibility for the outside firms that maintain safekeeping of billions in assets backing the products.

To date, Coinbase has been a leader in custody services for the U.S.’s exchange traded products (ETPs) – the wider universe that includes ETFs.

Anchorage Digital touted its legally required segregation of assets as a bank regulated by the Office of the Comptroller of the Currency, shielding such assets from the bankruptcy dangers seen in the recent past with the failure of crypto firms. It also said it’s using “industry-leading security and novel technology” to protect assets, including biometric authentication and offline private-key storage.

Custody has become an increasingly thorny problem in the crypto sector. The U.S. Securities and Exchange Commission has pursued a proposed rule requiring registered investment advisers to keep clients’ crypto assets with so-called “qualified custodians.” If the narrow definition pushed by SEC Chair Gary Gensler prevails, only a short list of firms inside the industry may qualify, including Anchorage Digital as a bank and such registered broker dealers as Prometheum Inc. and tZero Group Inc. (as of its announcement this week).