Can a transfer still be reversed after it shows as “successful”? That’s the question blockchain finality answers. The answer varies from chain to chain: Bitcoin relies on an increasing number of confirmations, Ethereum relies on staking votes, and some chains consider a block final as soon as it is produced.

Related coin: $ETH at 2390.87 (24h -3.49%).

What is finality?

Finality is the property that a confirmed transaction or block cannot be reversed or rewritten. Chains sometimes experience brief forks: when two blocks are produced at nearly the same time, only one branch is ultimately retained, and transactions in the other branch have to be queued again. Finality is about when you no longer need to worry about this happening.

Bitcoin: Probabilistic Finality:

Bitcoin has probabilistic finality. The more blocks are added on top of a block, the more blocks an attacker would have to recompute to reverse it, and the lower their chance of success. Section 11 of the Bitcoin white paper calculates how this probability drops rapidly as the number of confirmations increases.

So the commonly cited “wait for 6 confirmations” is a level of security generally accepted in practice, not something that is mathematically impossible to reverse. The number of confirmations needed can vary depending on the amount and the context.

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 holding two-thirds of the staked ETH vote to approve a checkpoint, it is first “justified” and then “finalized” in the next round. So blocks generally reach the finalized state after two epochs, or about 12.8 minutes.

To reverse a finalized block, an attacker would have at least one-third of their staked ETH slashed. 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 as Soon as They’re Produced:

Chains based on Tendermint (CometBFT) consensus, such as Cosmos Hub, have finality as soon as a block is committed, with 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 a transaction to reach the level of finality the platform considers safe. For large payments, wait for enough confirmations or finalization before releasing the funds. Deposits and withdrawals across different chains can take different amounts of time, and that doesn’t necessarily mean something has gone wrong.

My Take:

In a nutshell: “on-chain” doesn’t mean “set in stone.” Find out what counts as finality on the chain you use, and you’ll know how long to wait when making large transactions. If you’re unfamiliar with something, avoid going in with a large position at first; it’s safer to try a small amount.

If you have anything to add, share it in the comments.

Just some casual notes—make your own decisions when buying or selling.