| Reader situation | What to read | Planning use |
|---|---|---|
| You need the definition first | Fork, hard fork and soft fork basics | Settle the vocabulary before comparing chains, because only a permanent split leaves a separate coin behind. |
| You are comparing chains | Ethereum Classic versus Ethereum after the DAO fork | Use this to see which side kept the original history and which side adopted the fork. |
| You want to build or test | Geth and Ethash | Treat the Geth scripts and DAG step as a starting point for a private test chain. |
| You are asking why forks happen | Motives and holder outcomes | Judge a fork coin by the rule change it was created to make and by wallet support. |
The definitions and history in this table draw on ethereum.org’s fork documentation and a Changelly explainer on forks.
What is an Ethereum fork coin? It is the coin of a chain that split off when Ethereum’s protocol rules changed and not every participant followed, as Ethereum Classic did after the DAO fork.
Readers who want the wider family these chains belong to can start with what is a community coin, then return here for the Ethereum-specific technology.
When you need the definition first
Fork, hard fork and soft fork
Ethereum.org describes forks as changes to the rules of the Ethereum protocol, often planned technical upgrades. Clients must update their software to implement the new rules, and forks are usually agreed ahead of time so that clients adopt the changes in unison. Most forks are therefore routine upgrades, not new coins.
A hard fork is the kind that matters for this topic. Changelly explains that a hard fork introduces fundamental changes to a blockchain’s rules, and that old nodes see blocks built under the new rules as invalid and reject them immediately. A node that does not upgrade stays on the old rules and cannot follow the new chain.
A soft fork behaves differently. KuCoin’s overview notes that non-upgraded nodes can continue to participate without being split off, and that only changes which restrict or tighten what is considered valid can be deployed this way.
- Read it as an upgrade when the change was agreed in advance and every client updated together.
- Read it as a possible new coin when a hard fork leaves some nodes running the old rules and others running the new ones.
- Read it as no split at all when the change only tightens validity rules, since older nodes stay on the network.
When a fork becomes a separate coin
Ethereum.org states that, in rare cases, disagreements over forks can cause the network to permanently split. That permanent split is what produces a fork coin. Both chains keep the shared history up to the split and then follow different rules, so each develops its own coin, miners and community.
When you are comparing Ethereum Classic with Ethereum
Ethereum Classic: the chain that stayed
Ethereum.org names the creation of Ethereum Classic with the DAO fork as the most notable case of a permanent split. Changelly places the formation of Ethereum Classic after the DAO hack in 2016. The reason for the split was therefore a response to that hack, and the disagreement was about whether to change the chain’s history to restore affected funds.
Bitcoin Magazine’s commentary from the time adds that several miners, developers and stakeholders remained on the old blockchain, now called Ethereum Classic. For anyone comparing the two, Ethereum Classic is the continuation of the pre-fork chain, not a later copy of Ethereum.
Ethereum: the chain that adopted the fork
KuCoin reports that the majority of the network adopted the DAO fork, restoring the affected funds. That majority chain kept the Ethereum name. This is the sharpest answer to the question of how Ethereum Classic differs from an Ethereum fork: Ethereum Classic rejected the fork and kept the original rules and history, while the chain that followed the fork carried on as Ethereum.
- Choose Ethereum Classic if you want the chain whose community held to the original, unaltered history.
- Choose Ethereum if you want the chain most of the network moved to after the DAO fork.
- Check the chain name and wallet support before sending funds to either, since the two share early history but not current rules.
Planned upgrades are not splits
Ethereum keeps changing without splitting. Ethereum.org lists the Prague-Electra (Pectra) upgrade as activating on May 7, 2025, at 10:05:11 AM UTC. A dated, coordinated upgrade like this is the opposite of a contested split. Smaller chains weigh these choices differently, as community coins vs bitcoin and ethereum sets out.
When you want to build or test a fork
Geth and chain initialisation
Geth is an Ethereum client, and it is the software a community walkthrough in the fork-ethereum repository uses to stand up a new chain. The guide’s commands are the scripts init-genesis.sh, start-geth.sh and connect-geth.sh, which initialise the chain from a genesis file, start the node and connect nodes together.
This path suits developers who want to learn how a chain begins, or who want to test changed rules on a private network. It does not by itself give a fork any community, exchange listing or wallet support, and a private test chain is not the same as a split of the live network.
Ethash and mining on a Geth chain
The same walkthrough shows the Geth console generating the DAG and mining coins with miner.start() and miner.stop(). The DAG step is where Ethash enters a Geth-based chain, and it is why forks built from this code are often discussed as Ethash forks. Starting and stopping the miner from the console lets a tester produce blocks on a private chain without outside hardware.
- Use a private Geth chain to learn genesis files, node connections and block production.
- Expect extra work for anything public, because other nodes must choose to follow your rules.
- Keep the DAG step in mind when planning mining tests, since the guide lists it before mining begins.
When you are asking why projects fork
Changing the rules a community disagrees on
Projects fork when a group wants rules the existing chain will not adopt. Changelly’s account of Bitcoin Cash shows the pattern outside Ethereum: Bitcoin Cash launched in August 2017 and increased its block size to 8 MB, while Bitcoin kept smaller blocks. Ethereum’s case was different, a response to the DAO hack, but the mechanism is the same. A hard fork lets a group run its own rules on shared history.
Because clients must update to implement new rules, anyone who forks Ethereum code also takes on the job of getting clients, miners and users to move with them. That is the cost that separates a successful fork coin from a private experiment.
What holders receive
KuCoin notes that holders of Bitcoin at the time of its fork received an equivalent balance on the new chain. A hard fork can therefore give existing holders a matching balance on both sides, though the value and usability of each side depend on its own support. How supply and distribution are set on such chains is covered in community coin tokenomics explained.
Frequently asked questions
| Question | Answer |
|---|---|
| Does every hard fork create a new coin? | No. Ethereum.org says forks are usually agreed ahead of time and clients adopt them together. Only rare disagreements permanently split the network. |
| Can a soft fork split the network? | Not in the way a hard fork can. Non-upgraded nodes keep participating, and only changes that tighten validity rules qualify as soft forks. |
| What happens to nodes that do not upgrade for a hard fork? | They treat blocks built under the new rules as invalid and reject them, so they stay on the old rules. |
| Will a forked coin appear in my wallet automatically? | It depends on wallet and exchange support, according to Changelly, so check that your wallet supports the new chain. |