According to co-founder Vitalik Buterin, Ethereum can occasionally forgo finality without endangering the network extensively, even after a recent client bug nearly disrupted the blockchain’s confirmation process.
After a recent bug in the Prysm Ethereum client, Buterin remarked in an X post that losing finalization now and then is not an issue. He explained that finalization ensures the network is “certain” that a block will not be reverted.
Buterin maintained that if finality is delayed for hours due to a significant bug, “that’s fine,” as the blockchain continues to function during that period. He emphasized that the main concern should be finalizing incorrect information.
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Experts weigh in on finalization loss
Fabrizio Romano Genovese, PhD in computer science at the University of Oxford, England, partner at the blockchain research company 20squares, and an Ethereum protocol specialist, supported Buterin’s view.
He pointed out that losing finality makes Ethereum resemble Bitcoin (BTC), noting that Bitcoin has experienced “no finality since 2009 and no one complains.”
In a proof-of-work blockchain like Bitcoin’s, the network can diverge into several chains, with the longest one deemed valid. However, if a secondary branch accumulates enough strength to surpass the main branch, it invalidates it and its transactions — a process known as reorganization.
This reflects Bitcoin’s operation: its finality is probabilistic rather than deterministic because — while it’s virtually impossible after a certain number of blocks are appended to the main branch — a reorganization could still theoretically happen. Genovese clarified how Ethereum differs, having rules that classify blocks as “final.” He elaborated:
“Ethereum has a finalization mechanism: When a block receives over 66% of the validator votes, it is termed ‘justified.’ If more than two epochs (64 blocks) pass, the block becomes finalized.”
This is not merely theoretical; it occurred in May 2023 due to an event similar to the recent issue with the Prysm client. Genovese indicated that such incidents do not compromise the chain’s security; they simply mean that the guarantees regarding reorganization have temporarily shifted to being probabilistic rather than deterministic.
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Consequences for L2s and bridges
However, Genovese cautioned that a lack of finality would impact infrastructure dependent on it, including certain inter-blockchain or layer-2 (L2) bridges.
A representative from the Ethereum sidechain Polygon informed Cointelegraph that while operations would continue normally, transfers from Ethereum to the sidechain “may be delayed while waiting for finality.”
Moreover, the Polygon spokesperson mentioned that the crosschain settlement layer AggLayer would halt transactions from Ethereum to L2 until finality was reestablished. They reassured that “there is no scenario in which users experience a rollback or message invalidation” due to a finality loss:
“The practical impact of a delayed finality event is simply that deposits may take longer to appear. Users are not exposed to reorg-driven reversions beyond this delay.”
Genovese attributed the responsibility for such delays to developers who require finality. “If a bridge builder chooses not to implement any contingency mechanism in case of finality loss, that’s their decision,” he concluded.
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