The Altair hard fork, the first mainnet upgrade to the Ethereum (ETH)’s beacon chain, is slated to go into effect on October 27.
The update is considered a "low stakes warm-up" to the upcoming Merge, when the current Ethereum mainnet, which is secured by a proof-of-work (PoW) consensus mechanism, "merges" with the beacon chain proof-of-stake (PoS) system.
This upgrade brings light-client support to the core consensus, cleans up beacon state incentive accounting, fixes some issues with validator incentives, and steps up the punitive parameters, according to the Ethereum Foundation.
The Altair upgrade might be the only upgrade to the beacon chain, which went live in December of last year, before Ethereum transitions to the PoS consensus
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