Soft Fork

Definition

A soft fork is a change that tightens blockchain validation rules so that blocks accepted under the new rules remain acceptable under the older, less restrictive rules. Upgraded nodes enforce the additional conditions, while older nodes may continue following the same chain without understanding every new restriction. This compatibility relationship distinguishes a soft fork from a hard fork, which can allow blocks older nodes reject. Compatibility does not eliminate deployment risks or make adoption automatic. Participants still need an activation process and sufficient enforcement to avoid accepting histories that violate the intended rules. Bitcoin's SegWit and Taproot upgrades are examples of changes designed through soft-fork mechanisms. A software release, miner signal, and active consensus requirement are distinct events. Understanding a proposed soft fork therefore requires examining exactly which previously permitted behaviors become invalid and how participating nodes determine when to enforce that restriction.