This has been adapted from Coinbase
What is User Activated Hard Fork (UAHF), User Activated Soft Fork (UASF) and Segregated Witness?
There are two major proposals will affect the Bitcoin protocol and network known as UAHF and UASF. User Activated Hard Fork (UAHF), including Bitcoin ABC, is a proposal to alter the Bitcoin protocol by creating a new fork of the Bitcoin software, which will operate on its own, separate blockchain. In contrast, the User Activated Soft Fork (UASF), also known as BIP148, is a proposal to alter the Bitcoin protocol by merging new features into the Bitcoin software, but continue using the same existing blockchain. The proposed features for the upcoming UASF include Segregated Witness, a technology designed to increase the amount of transactions that can be made over the Bitcoin network, and increase the security of the network.
When will the Hard Fork or Soft Fork happen?
The UAHF is scheduled to activate on approximately August 1, 2017. The UASF is scheduled to activate at approximately the same time as the UAHF.
What happens to my BTC on BTC Markets?
The UAHF is incompatible with the current Bitcoin protocol and will create a separate blockchain. Should the UAHF activate on August 1, BTC Markets will not support the new blockchain or its associated coin. Any BTC within customers’ accounts will remain accessible over the main blockchain only, and will not be converted into BTC on the UAHF chain. The UASF will not alter any customer funds which are stored in BTC Markets
Do I need to withdraw my BTC from BTC Markets?
The UAHF will functionally create two different versions of Bitcoin. In contrast, the UASF will likely not create another version of Bitcoin. However, the UASF may initially cause instability on the Bitcoin network. To ensure the safety of customers’ funds, we will temporarily suspend BTC deposits and withdrawals starting July 31st at 12:00PM (GMT+10). Users that wish to access their coins on the UAHF chain or wish to access their funds immediately while the forks are happening should withdraw their BTC from BTC Markets to an external wallet address under their control before July 31st at 12:00PM (GMT+10). Deposits and Withdrawals will be resumed when it is deemed safe to do so.
Does this affect ETH, ETC, LTC or XRP?
No, ETH, ETC, LTC and XRP will continue as normal with deposits, withdrawals and trading unaffected.
Is there any risk to simply leaving my BTC in BTC Markets during this event?
No, there is no risk to your existing funds. Leaving BTC in your BTC Markets wallet will not change anything about your BTC. However, you should move your BTC off BTC Markets if you would like access to coins on the new UAHF chain.
Will BTC Markets allow trading during this time?
Yes. Trading will still be enabled during this time. It is only deposits and withdrawals that will be suspended.
Will BTC Markets eventually support withdrawals for the UAHF version of Bitcoin?
We will continue to monitor UAHF developments and advise accordingly.
Can you recommend which wallet software I should use if I want to withdraw my Bitcoin?
While we cannot recommend any particular third-party wallet, a helpful list of wallet options is available here: https://bitcoin.org/en/choose-your-wallet
Does BTC Markets support the UAHF? What about the UASF?
We support the growth and scaling of the Bitcoin network. Although we have no plans to support additional blockchains at this time, we will continue to monitor UAHF/UASF developments.