An issue with the Prysm consensus client on mainnet saw about 23% of the Ethereum network going offline.
In the early hours of Thursday, the Ethereum Foundation alerted the community about an issue with the Prysm consensus client on mainnet, urging node operators to reconfigure their CL nodes. This only affected those utilizing Prysm clients, with other network clients unaffected.
In a confirmation tweet, Ethereum client Prysm stated that it had identified the issue and promised a quick workaround. It urged dependent nodes to disable the Prysm client.
In a tweet, Ethereum angel investor and educator Sassal ETH revealed a shocking fact in the wake of this incident.
The bug on the Ethereum Prysm client had caused about 23% of the network to fall off. Sassal shared an image alongside his tweet, which indicated Prysm accounting for about 23% share of the Ethereum consensus clients.
Commenting on the data presented, Sassal noted it was accurate, with about 23% of the network going offline due to a bug with Prysm. He revealed a worse-case scenario, which would have happened if it were the Lighthouse client that had this issue.
According to the image, Lighthouse accounted for a 48.47% share of Ethereum consensus clients, with Sassal adding that the ETH network would have lost finalization if it were Lighthouse that had the bug instead, which is not a good instance for the Ethereum network.
Ethereum creator allays concerns
Ethereum creator Vitalik Buterin weighs in on the discussion, dispelling such fears. “Nothing wrong with losing finalization once in a while imo,” Buterin said.
Nothing wrong with losing finalization once in a while imo.
Finalization is for when we’re _really sure_ a block won’t be reverted. If finality delays a few hours when a major client has a bug, that’s fine. The chain keeps going during that time.
The thing to avoid is…
— vitalik.eth (@VitalikButerin) December 4, 2025
The Ethereum creator sheds further light on the context of finalization, saying: “Finalization is for when we’re really sure a block won’t be reverted.”
Buterin puts to rest concerns regarding the Prysm incident, saying, “If finality delays a few hours when a major client has a bug, that’s fine. The chain keeps going during that time. The thing to avoid is finalizing the wrong thing.”
Fusaka, Ethereum’s second upgrade in 2025, went live on the mainnet on Dec. 3, marking a significant milestone for the network.
