BIP 68 — Relative lock-time using consensus-enforced sequence numbers

BIP 68 (Relative lock-time using consensus-enforced sequence numbers) is a consensus soft fork that repurposes the transaction nSequence field to enforce relative timelocks — an input cannot be spent until its referenced output has aged a set number of blocks or amount of time. It activated in mid-2016 together with BIPs 112 and 113. Repository status: Deployed.

Debate relevance: Foundational for Lightning and other off-chain protocols that need 'dispute windows' measured from confirmation, not from a calendar date. Common misstatements: Confusing BIP 68 (transaction-level nSequence semantics) with BIP 112 (the script opcode that reads them); they activated together and are often cited interchangeably.