What is a hard fork?

What happens when some players change the rules, but the rest want to carry on as before?

Think of a board game whose new edition allows moves the old one forbids. Those playing by the old rules can’t accept those moves as valid. Something similar happens in a hard fork, meaning a non-backward-compatible split of the blockchain: nodes running the old software reject blocks that are accepted under the new rules.

To follow the new chain, node operators need to upgrade their software. The changes may concern block size, how transactions are validated or other network rules. Unlike a soft fork, compatibility with the old rules isn’t preserved here.

Why it matters

A hard fork can enable technical improvements that don’t fit within the existing rules. It doesn’t necessarily create a new coin. If the community follows the new version and the old one is abandoned, the network carries on without a permanent split into two active chains.

But if two groups keep going with different rules, separate networks emerge that share a common history up to the point of the fork. A well-known example is the split between Bitcoin and Bitcoin Cash. From then on, each chain records its own transactions.

We consider this distinction crucial: an agreed upgrade is one thing, a disagreement that divides the community is another. For a crypto holder, both the technical consequences and the support from wallets and exchanges differ.

What to watch out for

If you hold coins on an exchange, access to any second coin depends on its policy. In your own wallet, you may need compatible software. Never give your seed phrase (recovery phrase) to websites that promise to “unlock” coins from a fork for you.

Some splits also carry the risk of a replay attack: a transaction on one chain may also be valid on the other if proper protections aren’t in place. Before moving coins, check the guidance from the network and your wallet.