The Bitcoin Segwit2x fork is projected to take place on November 16th and will temporarily result in two bitcoin blockchains. Following the fork, Coinbase will continue referring to the current bitcoin blockchain as Bitcoin (BTC) and the forked blockchain as Bitcoin2x (B2X).
Any customer with a BTC balance on Coinbase at the time of the fork will be credited with an equal amount of the B2X asset on the Bitcoin2x blockchain. No action is required — they will automatically credit your account. So, if you have 5 BTC stored on Coinbase before the fork; you will have 5 BTC and 5 B2X following the event.
Bitcoin2x Timeline
Approximately 24 hours pre-fork. Coinbase will temporarily disable all bitcoin buy, sells, sends and receives. ETH and LTC will not be impacted. You will still be able to see your Bitcoin balances and monitor the price. If you plan on moving BTC into your Coinbase account, i highly recommend that you do so at least 24 hours before the fork to ensure your transfers are confirmed.
Fork (block 494,784). Any Coinbase customer with a confirmed Bitcoin balance at this point will be credited an equal amount of Bitcoin2x.
Within 24 hours post fork. Coinbase customers will be able to buy and sell both Bitcoin and Bitcoin2x. When you visit Coinbase.com or open your Coinbase app, you will see your new Bitcoin2x balance (in Accounts).
Approximately 24–48 hours post fork. Once this ensured that the blockchains are stable, Coinbase will re-enable Bitcoin and Bitcoin2x sends and receives. Please be careful when sending funds as certain wallets and bitcoin services may refer to the two blockchains differently.