UASF (User-Activated Soft Fork)

A User-Activated Soft Fork (UASF) is a method of deploying a Bitcoin consensus change in which ordinary full nodes — not miners — enforce the new rules starting at a predetermined block height or date. It inverts the usual model: instead of waiting for a supermajority of hash rate to signal readiness, the economic majority running the software simply begins rejecting blocks that violate the new rule set, forcing miners to follow or risk having their blocks orphaned.

The BIP148 precedent

The best-known UASF was BIP148, deployed in 2017 to break a long stall over SegWit activation. Nodes running BIP148 were configured to begin rejecting, from 1 August 2017, any block that did not signal support for SegWit. Because miners depend on the economic network to value the coins they produce, the credible threat of a chain split pressured them to activate SegWit through the existing miner-signaling path before the UASF deadline arrived.

Why it matters for sovereignty

UASF is the clearest demonstration that, in Bitcoin, the rules are ultimately defined by the nodes that validate them rather than by the entities that produce blocks. Running your own fully validating node is how an individual participates in that enforcement. The approach is not without risk — a poorly supported UASF can cause a persistent chain split — which is why later activations explored alternatives such as BIP8 (lock-in by height) and the Speedy Trial used for Taproot.

UASF is one mechanism within Bitcoin's broader upgrade toolkit. Compare it with the miner-signaled soft fork and the rules-breaking hard fork to see where node-led enforcement fits.