What Is a Soft Fork, and How Does It Differ from a Hard Fork in Blockchain Upgrades?

A soft fork is a backward-compatible blockchain protocol upgrade, meaning non-upgraded nodes will still see new blocks as valid, though they may not fully validate the new rules. The upgrade is enforced by the majority of miners.

A hard fork, conversely, is a non-backward-compatible upgrade, where non-upgraded nodes will see new blocks as invalid, leading to a permanent split in the blockchain if not universally adopted. Soft forks are generally less disruptive and safer to deploy.