Bitcoin Classic , an attempt to implement an alternative version of the Bitcoin protocol with a higher block size limit, has been one of the biggest stories in the blockchain space over the past few months, and one of the key areas of debate over this new software client has to do with the 75 percent network hashrate activation threshold for a potential hard fork .
Many contributors to Bitcoin Core think the 75 percent number chosen by the Bitcoin Classic team is too low, but the reality is that the hard fork is likely to activate at a level of support more than three percentage points lower.
Bitcoin XT Background
Neighborhood Pool Watch is a popular Bitcoin mining blog operated by blockchain researcher Andrew Geyl . In August, Geyl made a post regarding some potential flaws in BIP 101 , which was the block size increase proposal implemented by Bitcoin XT . One of the flaws pointed out by Geyl was that there was no expiration date on voting for Bitcoin XT in coinbase transactions . This means, theoretically, voting could continue forever.
In both Bitcoin XT and Bitcoin Classic, the real method of hard fork activation is a count of miner votes from the last 1,000 blocks. If 750 of the last 1,000 blocks are found by miners who support the new, alternative protocol, then the hard fork is activated (although it doesn’t actually take place until after a grace period). The problem here — at least in terms of gauging miner support — is that miners can get lucky and find more blocks than their actual share of the network would predict over the short term.
As an example of this issue in his post from August, Geyl noted:
“After a couple of years (if voting continued for so […]
