Soft fork

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A soft fork (softfork) is a change to the cryptocurrency protocol wherein only previously valid blocks/transactions are made invalid. Since old nodes will recognize the new blocks as valid, unlike hard fork, a soft fork can still work with older versions of protocol. If a wallet wants to support new soft fork rules it has to be upgraded.

See also bitcoin wiki page


Soft forks in Bitcoin:

  • Introducing the limit of 1MB for block was done through a soft fork
  • The pay-to-script-hash function, which enhances the code without changing the structure was also successfully added through a soft fork.
  • SegWit was implemented in Bitcoin protocol using soft fork in BIP141.

Trezor started supporting SegWit in August 2017

See also this article for more information about differences between soft forks and hard forks.


When a majority of miners upgrade to enforce new rules, it is called a miner-activated softfork (MASF). When full nodes coordinate to enforce new rules, without support from miners, it is called a user-activated softfork (UASF).

See also Fork, Hard fork, Coin split