Finality

Finality is the moment at which a transaction is considered permanently recorded on a blockchain and can no longer be reversed by ordinary means. For end users it answers “when can I treat this transfer as actually done?”, for exchanges “when can I credit a deposit without rollback risk?”, and for application developers “when can I update off-chain state based on this on-chain fact?”.

Probabilistic finality (Bitcoin)

In Bitcoin and early Ethereum, finality is probabilistic. The block that includes a transaction can be replaced by a longer alternative chain if an attacker has enough hashrate. The more blocks stacked on top, the lower the chance of a rollback. That is why exchanges traditionally wait six confirmations on Bitcoin (around an hour) and dozens on legacy Ethereum. There is no strict “now it is final” point in this model — only a steadily decreasing probability of reversal.

BFT instant finality (TON, Cosmos)

BFT-based chains work differently. A block is either signed by a qualified majority of validators (more than two-thirds) or it is not. Once it is signed, it is final immediately: rolling it back would require more than one-third of validators to violate the protocol in coordination, which slashes their stakes and publicly records the attack.

TON belongs to this family. Catchain consensus signs each block once, and after a successful masterchain commit the block is irreversible under honest network operation.

Block time in TON

TON produces blocks quickly: the average masterchain interval is on the order of a few seconds (about five seconds in normal operation, shards can be faster). That means the time from posting an external message to seeing it finalised is usually only a handful of seconds under normal load. The Tonkeeper and similar wallet experience reflects this: hit send, watch the status flip to confirmed in a couple of seconds.

What this means in practice

• Exchanges. Toncoin deposits are credited after one or two blocks, with no long confirmation wait.
• DeFi. Liquidators and arbitrage bots can act on a fresh block without worrying that a reorg will rewrite the rules.
• Wallets. UIs can confidently show success once the lite-server confirms inclusion.

When finality can still be threatened

In theory even a BFT chain can halt: if more than one-third of validators go offline, the network stops producing new blocks, though the finality of already-signed blocks remains. A reorg deeper than a single block does not happen in TON under normal operation; the only scenario is a massive coordinated protocol violation by validators, which is detected immediately and penalised by slashing.

A practical shorthand for TON finality is “one block and that is it — no rollbacks”.