Soft Fork

A soft fork is a backward-compatible change to a blockchain's rules that only tightens what counts as valid, so nodes still running older software continue to accept the new blocks. Because upgraded and non-upgraded participants remain on a single chain, a soft fork usually avoids the permanent split risk of a hard fork, though it still needs enough miners or validators to enforce the stricter rules. Bitcoin's SegWit and Taproot upgrades were deployed as soft forks. The trade-off is that soft forks can only restrict, never expand, the existing rule set, and older nodes may accept transactions whose new rules they cannot fully verify, so they effectively rely on upgraded nodes for the newer guarantees.