Coinbase says it will "evaluate any potential forks"

According to Coinbase if an Ethereum  Proof of work fork occurs after

the Merge, this asset will be examined with the same scrutiny 

as every other asset listed on our exchange. 

Exchanging cryptocurrencies to account for potential 

forks, Coinbase has updated its information about Ethereum's switch

to proof-of-stake. The cryptocurrency exchange Coinbase

previously announced its intention to "briefly pause" deposits and

withdrawals of ERC-20 tokens and Ether (ETH) during the Merge, which

is anticipated to take place between September 10 and 20.

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