User-Activated Soft Fork (UASF) and Miner-Activated Soft Fork (MASF)
Two paths for activating a soft fork: a UASF relies on node operators and users enforcing new rules directly, while an MASF relies on miners signaling majority support first.
A Miner-Activated Soft Fork, or MASF, is the conventional path for activating a soft fork (see Kaavon's "Soft Fork" glossary definition): miners signal their readiness to enforce new rules, and the change activates once a sufficient majority of mining power signals support. A User-Activated Soft Fork, or UASF, is an alternative path that instead relies on node operators and users themselves committing to enforce the new rules at a predetermined date, regardless of whether miners have signaled support, betting that enough economic weight (node operators, exchanges, and users) will follow along that miners are effectively forced to comply to avoid having their blocks rejected.
A UASF represents a notable statement about where ultimate authority over a blockchain's rules actually resides — it asserts that node operators and economic participants, not miners, are the final arbiters of consensus rules, since miners who refuse to comply risk having their blocks rejected by UASF-enforcing nodes. The UASF movement was most prominently used during Bitcoin's 2017 SegWit (see Kaavon's "SegWit" glossary definition) activation, where mounting UASF momentum is widely credited with pressuring miners into signaling support before the UASF's own activation deadline arrived.
Examples
- Bitcoin's 2017 UASF movement for SegWit activation is widely credited with pressuring miners into signaling support before the UASF's own deadline, avoiding a potential chain split.
- A UASF asserts that node operators and economic participants, not miners, hold the final say over a blockchain's consensus rules, in contrast to the conventional miner-signaling MASF path.