After a transfer is marked “successful,” could it still be reversed? That’s the question “finality” answers in blockchain. Different chains have different answers: Bitcoin relies on more and more confirmations, Ethereum on staking votes, while some chains consider a block final as soon as it’s produced.
On Ethereum, staked $ETH is what guarantees finality: rewriting a finalized block would result in the loss of a large amount of stake. Current price: 2245.66 (24h -7.42%).
What is finality?
Finality is the property that a confirmed transaction or block cannot be reverted or rewritten. Chains can occasionally experience brief forks: when two blocks are produced almost simultaneously, only one branch is ultimately retained, and transactions in the other branch have to be queued again. Finality tells you when you no longer need to worry about this happening.
Bitcoin: Probabilistic Finality:
Bitcoin has only probabilistic finality. The more blocks are stacked on top of a block, the more blocks an attacker would have to recompute to overturn it, and the lower the chance of success. Section 11 of the Bitcoin white paper calculates that this probability drops rapidly as the number of confirmations increases.
That’s why the commonly recommended “wait for 6 confirmations” is a level of security widely accepted in practice, not a mathematical guarantee that a block can never be overturned. The required number of confirmations can vary depending on the amount and the situation.
Ethereum: Finality:
Ethereum’s proof-of-stake system uses the Casper FFG mechanism. Every 32 slots make up an epoch, which lasts about 6.4 minutes. Once validators representing two-thirds of the staked ETH vote to approve a checkpoint, it is first “justified” and then “finalized” in the next round. As a result, blocks generally reach the finalized state after two epochs, or about 12.8 minutes.
To overturn a finalized block, an attacker would lose at least one-third of all staked ETH to slashing. This is economic finality: it’s not impossible, but the cost is extremely high. If too many validators go offline, finalization pauses, but block production continues.
Chains Where Blocks Are Final Upon Creation:
On chains that use Tendermint (CometBFT) consensus, such as Cosmos Hub, a block is final as soon as it is committed; there’s no need to wait for subsequent blocks. The trade-off is that validators must go through multiple rounds of voting for every block, and communication overhead increases as the number of validators grows.
What This Means for Everyday Users:
The number of confirmations an exchange requires for a deposit is essentially how long it waits for the transaction to reach a level of finality the platform considers safe. When receiving a large payment, wait for enough confirmations or for finalization before releasing it. Deposits and withdrawals across different chains can take different amounts of time, and a delay doesn’t necessarily mean something is wrong.
A Final Word:
In short: “on-chain” doesn’t mean “set in stone.” Understand what counts as finality on the chain you use, and you’ll know how long to wait when making a large transaction. Understanding the principles helps you make more informed decisions; it isn’t a way to predict market movements.
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