Segregated Witness support has been locked-in as a soft fork expected to activate around August 23rd, 2017 (block height 481,824).
Now Segwit2x developers confirm that the Bitcoin upgrade is to happen at block 494,784.
During the month of November 2017, approximately 90 days after the activation of Segregated Witnesses in the Bitcoin blockchain, a block between 1MB and 2MB in size will be generated by Bitcoin miners in a move to increase network capacity. At this point it is expected that more than 90% of the computational capacity that secures the Bitcoin network will carry on mining on top of this large block.
According to the report, the November 2017 upgrade to 2MB blocks is a hard-fork, but necessary changes are trivial to perform. Some SPV clients are expected to work without any change at all. Most clients will need to tweak only two constants to remain compatible with the new larger blocks:
For SegWit-compatible clients:
- Maximum block weight doubles from 4,000,000 to 8,000,000
- Sig-ops per block doubles from 80,000 to 160,000
For non-SegWit-capable clients:
- Maximum base block size doubles from 1,000,000 to 2,000,000
- Sig-ops per block doubles from 20,000 to 40,000
Both types of clients should add new DNS seeds:
- BitPay: seed.mainnet.b-pay.net
- OB1: seed.ob1.io
- Blockchain: seed.blockchain.info
- Bloq: bitcoin.bloqseeds.net
For testing purposes, a new Testnet5 network that builds on the same Genesis block as the existing Testnet3 network has been created, as the report claims. In order to update a client for compatibility with Testnet5, do these changes to existing Testnet3 settings:
- Port changes from 18333 to 18555.
- Network magic changes from
- BIP-34, BIP-66, BIP-65 and single checkpoint all refer to the block at height 10001 with hash
- DNS seeds are available at
Block size/weight and sig-ops changes above also apply to Testnet5.
Compatible Fully-Validating Node Software
- BTC1: https://github.com/btc1/bitcoin
- Bitcoin Unlimited: https://www.bitcoinunlimited.info/
- Bitcoin Classic: https://bitcoinclassic.com/
Incompatible Fully-Validating Node Software