At block 494,784 the bitcoin blockchain will hard fork into 2 distinct chains, one supporting larger blocks up to 2MB, and another keeping the historical limit of 1MB. The fork will occur simply by emitting a block larger than 1MB (with Segwit discount). The current expected calendar date for that block to be mined is sometime between Nov. 15th and Nov. 16th.

BlockCypher will support both chains at the time of the fork and we do not expect any service interruption. Here is how we plan to address it:

Web services for the current 1MB chain will stay under its current endpoint at https://api.blockcypher.com/v1/ btc/main so users who do not want to change anything in the way they support bitcoin can do so without any update.

so users who do not want to change anything in the way they support bitcoin can do so without any update. The Segwit 2x hard fork will be available under https://api.blockcypher.com/v1/ b2x/main around Nov. 9th, leaving users time to try it out and test. Note that as for any blockchain we support, the API will be identical: only 2 characters in the URL need to change. For the first week of existence of this new b2x chain, it will have the exact same blocks and transactions as the btc chain.

around Nov. 9th, leaving users time to try it out and test. Note that as for any blockchain we support, the API will be identical: only 2 characters in the URL need to change. For the first week of existence of this new b2x chain, it will have the exact same blocks and transactions as the btc chain. No customer-specific data will be copied from one chain to the other (i.e. webhooks, payment forwards, wallets, etc). This is to avoid surprises, for example: 2 webhooks triggering on each chain without knowing from which it was for as they would share the same id or customers getting webhook notifications for a chain they don’t want to support. As a result, you should create the webhooks, forwards or wallets you’re interested in on the b2x chain. The only exception to this will be for BlockCypher’s enterprise customers: if you want us to mirror your data, you must contact us no later than Nov. 9th.

While all our services will remain available during the fork, there are some considerable challenges due to the absence of replay protection on the b2x fork. This unfortunately prevents us from automatically protecting all our API users against transaction replay. However we can advise customers on how to proceed on a case by case basis and we will try to obtain forked coins as soon as possible after the hard fork.

Obviously, the situation is extremely fluid. Please come back here regularly in the days preceding the fork for potential updates and follow us on Twitter for emergency notices.