UBS, the Zürich-based banking giant, will let some clients who desire to trade bitcoin ETFs do so, subject to some conditions, according to a person familiar with the matter.

The conditions, according to the person close to UBS who asked to not be named, include: UBS cannot solicit the trades and accounts with a lower risk tolerance won't be able to buy them.

A UBS spokesperson declined to comment.

Citigroup, meanwhile, “currently provides our institutional clients with access to the recently approved Bitcoin ETFs from an execution and asset servicing perspective," a spokesperson told CoinDesk Thursday. The New York-based global bank is "evaluating the products for individual Wealth clients.”

Bitcoin ETFs debuted to enormous excitement on Thursday, with billions of dollars worth traded on the first day they were available.

Vanguard, the large U.S.-based investment firm, said Thursday it would not let customers trade them. There were unconfirmed rumors earlier in the day that UBS and Citi might join Vanguard in not offering them.

Some of the largest names in finance are offering bitcoin ETFs, including BlackRock, Fidelity and Invesco. And Charles Schwab, the large U.S. brokerage, confirmed to CoinDesk on Thursday that it will let clients trade them.

Optimists believe bitcoin ETFs will dramatically broaden the investor base for bitcoin, since buying ETFs is easier than purchasing bitcoin itself.

UPDATE (Jan. 1, 00:05 UTC): Adds details about Citi throughout.