Finality
consensus · blockchain
The rules or confidence used to judge whether a confirmed transaction can still be reversed.
Finality describes resistance to reversing confirmed state. Proof-of-work chains usually provide probabilistic finality: additional accumulated work makes a reorganization less likely and more costly but does not create one universally irreversible height.
Some proof-of-stake and Byzantine-fault-tolerant systems define checkpoints as finalized after a required validator threshold signs or votes. Those guarantees depend on the protocol's fault assumptions, validator set, slashing or recovery rules, and whether clients accept an emergency override.
Services choose confirmation requirements based on value, available hash rate or stake, reorganization history, fraud signals, settlement dependencies, and their tolerance for delay. An unconfirmed acceptance policy is a risk decision, not consensus finality, even when wallets provide conflict alerts or double-spend proofs.
Related terms
Confirmations
→The count of blocks confirming a transaction, usually including the block that first contains it.
security · blockchain
Chain Reorganization
→A network event where the active chain tip switches to a different branch with more accumulated work.
blockchain · security
Proof of Work (PoW)
→A consensus mechanism that makes block production require verifiable computational work.
mining · blockchain · consensus
Proof of Stake (PoS)
→A family of consensus mechanisms in which validators commit stake to propose, attest to, and finalize blocks.
consensus · blockchain