What Is a ‘Soft Fork’ versus a ‘Hard Fork’ in Blockchain Upgrades?
A soft fork is a backward-compatible protocol upgrade, meaning old, non-upgraded nodes will still recognize new blocks as valid, even if they don't understand the new rules. A hard fork is a non-backward-compatible upgrade that requires all nodes to update; if not, the network permanently splits into two separate chains with different rules.
Hard forks are often used for major changes.
