Forks, hard and soft
How a network with no management changes its own rules. When agreement fails, the chain splits and both halves carry on.
There is no committee that can amend the rules of an open blockchain. Changes happen by persuading enough participants to run new software, and the shape of that change determines whether the network stays together.
Soft fork
A soft fork tightens the rules. Blocks valid under the new rules remain valid under the old ones, so nodes that have not upgraded continue to accept the chain.
This makes upgrading voluntary in the short term and is the preferred route for conservative changes. Bitcoin's SegWit in 2017 and Taproot in November 2021 were both soft forks.
Hard fork
A hard fork loosens or alters the rules so that new blocks are invalid under the old software. Every participant must upgrade, or be left behind on a different chain.
Both continue producing blocks. Both share an identical history up to the split. Everyone holding a balance before the split holds the same balance on both chains afterwards, because the history containing it is common to both. This is how Bitcoin Cash came into existence on 1 August 2017, and how Ethereum Classic came into existence in July 2016.
The part that confuses people
A split does not duplicate value; it divides a community. Both chains inherit the ledger, and the market then decides what each is worth — frequently a great deal for one and very little for the other. Receiving "free coins" from a fork is not a windfall so much as a claim on whichever fragment of the network survives.
Coordination in practice
- Ethereum upgrades on a roughly annual cadence through planned hard forks, with implementation coordinated among client teams and an activation block agreed in advance. Recent upgrades have run to schedule.
- Bitcoin changes rarely and prefers soft forks, with activation mechanisms designed to measure support before a change locks in.
- Both depend ultimately on the same thing: enough independent operators choosing to run the new code. See nodes and clients.
In a system with no way to vote and no authority to defer to, the ability to leave is the constitutional right. Anyone who disagrees strongly enough can run different rules and take whoever agrees with them. That is genuinely decentralised, and it means disputes are settled by schism rather than by process — which is costly, slow, and hard on anyone caught in the middle.
Practical notes for a holder
During a contentious split, transactions can be valid on both chains, which has historically caused people to send on one chain and unintentionally move a balance on the other. Wallets add replay protection to prevent this, and it is not always immediate. The safe behaviour during a split is to do nothing for a while.