We wanted to provide customers notice of how a possible hard fork of the Bitcoin protocol into Bitcoin Core and Bitcoin Unlimited will affect Coinbase accounts.

The only version of Bitcoin supported on the Coinbase platform today is Bitcoin Core, currently represented by the symbol BTC.

We may provide support for Bitcoin Unlimited in the future depending on market conditions and stability of the protocol, but we cannot guarantee whether or when such support may be available. Customers who wish to access both blockchains at the time of the hard fork should withdraw their BTC from Coinbase since we cannot guarantee what will happen during the hard fork or when this access may be available.

If one chain receives an overwhelming majority of support from miners, users, and exchanges, we reserve the right to alter the names of chains or discontinue support for certain chains in the future.

Eoin Treacy's view

This is not exactly great news for investors in bitcoin since the essence of the platform is that the blockchain is inalienable and now they find that there are going to be two blockchains. 

A significant number of investors have bought bitcoin on the assumption demand will continue to rise which it has but this announcement introduces potentially terminal uncertainty since no one knows what version of blockchain the majority will migrate into. 

In the aftermath of the hard fork event the potential crisis will be resolved but in the meantime there is ample potential for prices to fall. So far the $1000 area has represented at least a short-term area of support but the uptick in volatility over the last month is representative of churning and is an additional sign supply may be achieving dominance.