Soft Fork

Technically, a soft fork works by tightening the rules a network already follows rather than loosening them. Because the new rule set is a subset of what old software still accepts, unupgraded nodes keep validating the chain correctly, they simply cannot enforce or take advantage of the new feature themselves. This is what keeps the network on a single chain instead of splitting into two, which is the defining risk of a hard fork.

Two activation styles are common. In a miner-activated soft fork (MASF), a supermajority of miners signal readiness in mined blocks before the change locks in. In a user-activated soft fork (UASF), node operators and exchanges coordinate to enforce the new rules on a set date, pressuring miners to follow along regardless of their own signaling. Bitcoin has used both approaches: SegWit combined miner signaling with UASF pressure in 2017, while the 2021 Taproot upgrade, bundling Schnorr signatures, a new output type, and an updated scripting language, locked in through near-unanimous miner signaling under the "Speedy Trial" method without controversy.

• Pay-to-Script-Hash (P2SH), which enabled multisignature addresses
• SegWit, which restructured transaction data to raise effective block capacity
• Taproot, which improved privacy and reduced fees for complex transactions

Because a soft fork only needs majority, not universal, agreement to activate, it is the preferred route for protocol changes where broad consensus is achievable but not guaranteed from every participant.