Definition
Block finality is a blockchain concept describing when a block and its included transactions are considered permanently accepted by the network. At the point of finality, the probability that the block will be removed or replaced through a reorg becomes negligible. Different consensus mechanisms define and achieve finality in different ways, but the core idea is that the ledger state at that block is effectively immutable. Finality provides a clear boundary between tentative and settled transaction history.
In probabilistic systems, finality is often associated with accumulating block confirmations, which reduce the likelihood that an alternative chain will overtake the current one. In systems with stronger guarantees, finality can be explicitly signaled by the consensus protocol, after which reverting a block would require violating protocol assumptions. Regardless of the approach, block finality is a key property that underpins trust in transaction settlement and the reliability of the on-chain record.
Context and Usage
Block finality is closely tied to consensus, because it reflects the point at which network participants agree that a specific chain of blocks is the canonical history. Before finality, blocks may be valid but still vulnerable to replacement if an alternative chain gains more support. After finality, changing the accepted history would typically require extreme conditions, such as overwhelming control of consensus resources or protocol failure.
The notion of finality also frames how block confirmation counts are interpreted in practice. A higher number of confirmations is treated as a proxy for stronger effective finality, since it becomes harder for a reorg to reach deeper blocks. As a result, block finality serves as a conceptual measure of settlement assurance, distinguishing between recent, potentially reversible blocks and deeply embedded, practically irreversible ones.