A soft fork (soft fork) is a change to a cryptocurrency's protocol rules that preserves backward compatibility with older versions of the software. With a soft fork, the new rules make some previously valid operations invalid, but nodes that have not updated their client still perceive the new blocks as correct. Because of this, the network does not split into two independent chains.

A soft fork is contrasted with a hard fork — a hard update that breaks compatibility and, in the absence of unanimity, can lead to the emergence of two separate blockchains. A soft fork, on the other hand, is considered a smoother way to roll out improvements, since activation usually only requires the support of the majority of those who produce blocks.

Features of a soft fork

• Backward compatibility with older nodes is preserved.
• The protocol rules become stricter rather than broader.
• It does not require all network participants to update simultaneously.

Soft forks are used to add new capabilities and improve security without splitting the community. Their successful rollout depends on the agreement of a significant share of the participants who sustain the network's operation.