Finality in blockchain refers to the point at which a transaction is considered irreversible and permanently part of the blockchain. Once a transaction has finality, it cannot be changed, canceled, or double-spent it’s guaranteed to be part of the canonical chain

There are two main types of finality:

1. Probabilistic Finality:

i). Used in blockchains like Bitcoin and Ethereum (pre-Merge).

ii). A transaction becomes more "final" as more blocks are added on top of it.

There's always a small chance of a chain reorganization, so finality is not 100% guaranteed, but becomes extremely unlikely over time (e.g., 6 confirmations in Bitcoin is generally considered final).

Deterministic (or Absolute) Finality:

1. Used in proof of stake systems with Byzantine Fault Tolerance (BFT) algorithms (e.g., Ethereum 2.0, Tendermint, Polkadot).

2. Once validators agree and finalize a block, it’s impossible to reverse without significant validator misbehavior (usually with slashing penalties).

3. Finality is instant and guaranteed once reached.

Irreversible Confirmation:

Finality signifies that a transaction has been successfully validated and confirmed by the blockchain network, making it impossible to reverse or change.

Guaranteed Security:

The finality of transactions is a critical aspect of the security and reliability of blockchain systems, as it prevents fraudulent activities or disputes over the validity of a transaction.

Consensus Mechanisms:

Finality is achieved through consensus mechanisms like Proof-of-Work (PoW) or Proof-of-Stake (PoS), which involve a network of validators reaching agreement on the validity of a transaction before it's added to the blockchain.

Probabilistic vs. Deterministic Finality:

Some blockchains offer probabilistic finality, where the likelihood of a transaction being reversed decreases as more blocks are added to the chain, while others provide deterministic finality, offering an immediate guarantee of permanence.

Foundation for Trust:

Finality plays a vital role in building trust and confidence in blockchain technology, as it assures users that their transactions are secure and irreversible.

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