Hard fork

What is Hard fork?

A hard fork is a radical change to a blockchain protocol that renders previously invalid blocks and transactions valid - or vice versa - and requires all nodes or users to upgrade to the latest version of the software. This kind of upgrade is not backward-compatible, meaning that nodes running the old version will no longer be accepted by the new version of the network. As a result, the blockchain splits into two separate and independently functioning chains: one that follows the original set of rules, and another that follows the updated protocol. This divergence leads to the creation of two distinct networks, each with its own transaction history and potentially its own cryptocurrency.

Hard forks may be planned or contentious. Planned forks are typically the result of consensus within the development and user community to implement protocol upgrades, add new features, or fix vulnerabilities. In contrast, contentious forks arise when disagreements emerge over proposed changes - such as scalability solutions or block size adjustments - leading to the formation of competing chains backed by different groups of users and miners.

Notable examples include the Bitcoin and Bitcoin Cash split, as well as Ethereum and Ethereum Classic. Unlike soft forks, which are backward-compatible, hard forks require all participants to upgrade to the new version to continue interacting with the updated network.