Last Irreversible Block

The Last Irreversible Block (LIB) is the most recent block in a blockchain that has achieved finality and cannot be reversed or reorganized through any consensus mechanism rules. In Delegated Proof of Stake systems and similar consensus protocols, a block becomes irreversible once it has been confirmed by a supermajority of validators or witnesses, typically two-thirds or more of active participants. Once a block reaches this status, the transactions it contains are considered permanently settled, and network participants can confidently treat that data as immutable. The concept of irreversibility provides economic and cryptographic guarantees that go beyond simple confirmation counts. Blocks that have not yet reached irreversibility remain vulnerable to reorganization if consensus participants act maliciously or if network conditions change dramatically. Example: On the EOS blockchain, which uses Delegated Proof of Stake, a block becomes irreversible once 21 elected block producers have all confirmed subsequent blocks, typically occurring within seconds of block production. Why it matters for blockchain technology: Last Irreversible Blocks enable finality guarantees essential for settlement, cross-chain communication, and user confidence. Knowing exactly which blocks are permanently settled helps dApp developers build reliable systems and allows exchanges to credit deposits with certainty, reducing the security assumptions users must make.

Category: blockchain technology

Explore the full Web3 Glossary — 2,062+ expert-curated definitions. Need guidance? Talk to our consultants.