BIP 8 (Soft Fork Activation)

BIP 8 is a Bitcoin improvement proposal that defines a method for activating soft forks, designed as a successor to BIP 9 after the difficult segwit activation of 2017. It measures signaling periods in block heights rather than timestamps and includes an optional setting, lockinontimeout, that guarantees the upgrade activates at the end of the signaling window even if miners never reach the signaling threshold.

Why it matters

BIP 8 is at the center of one of Bitcoin's deepest governance questions: who decides when the rules change. Under BIP 9, miners could block an upgrade indefinitely by declining to signal, which many saw during the segwit stalemate as a veto that miners were never meant to hold. BIP 8 with lockinontimeout set to true removes that veto, putting final authority with the nodes and users who choose to run the software. Critics counter that a guaranteed activation risks a chain split if a meaningful share of the network does not upgrade.

How it works

A deployment moves through defined states: it starts, miners signal readiness in the block version field, and if signaling reaches the threshold within a retarget period the fork locks in and then activates. If the timeout height arrives without lock-in and lockinontimeout is true, blocks must signal in the final period, forcing activation. Taproot in 2021 ultimately used a variant called Speedy Trial, which borrowed height based parameters from BIP 8 while leaving the mandatory activation question unresolved.