In a blog post, Coinbase stated their decision came after careful review. Ensuring the security of Bitcoin Cash's network was a priority, as was evaluating customer demand, trading volumes, and regulatory considerations. But the exchange wanted to be clear that "both bitcoin and Bitcoin Cash remain safely stored on Coinbase," and "that customers with balances of bitcoin at the time of the fork now have an equal quantity of bitcoin cash stored by Coinbase."

Assuming no great risks emerge, Coinbase says it will start supporting Bitcoin Cash on January 1st, 2018. Once that happens, customers will be able to withdraw their new cryptocoins -- but until then, they'll stay safely locked away.