Tim Beiko of the Ethereum Foundation projected this week that the Merge – Ethereum’s long-anticipated transition to a new design – might take place the week of Sept. 19.

The Merge will see Ethereum switch from the energy-intensive proof-of-work (PoW) consensus mechanism brought to the fore by Bitcoin to a more efficient proof-of-stake (PoS) system. In addition to slicing the network’s energy use by 99.95%, some proof-of-stake proponents believe that switching mechanisms will introduce security and scaling benefits.

Beiko, an Ethereum protocol support engineer, made his September estimate at a PoS Implementers Call. In addition to offering a potential date for the Merge, Beiko gave a timeline for other major Ethereum development milestones.

Though he offered a rare hard date for the Merge, Beiko has repeatedly noted – on Discord, Twitter and an Ethereum community Zoom call – that the timeline is very likely to change.

What is the Merge?

Today’s PoW mechanism, whereby miners compete to secure the network by solving complex computational puzzles, is the consensus algorithm that secures the Bitcoin blockchain, but it has been criticized for its high energy costs.

PoS – versions of which have already been adopted by chains like Solana and Tezos – replaces miners with validators. Validators can stake 32 ETH with the Ethereum network for the chance to get randomly selected to add blocks (bundles of transactions) to the chain.

In both PoW and PoS, adding blocks to the chain typically grants some rewards to the block issuer.

The update from PoW has been on Ethereum’s roadmap since it first launched in 2015, but engineering complexities have caused the shift – originally dubbed “Ethereum 2.0” – to drag out several years.

The Merge is not expected to reduce Ethereum’s relatively high fees and slow transaction speeds, but it will have a significant immediate impact on the network’s energy use.

Last week, Ethereum’s Sepolia testnet successfully switched to PoS. Goerli, the third and final of three public testnets, will run through the Merge process on Aug. 11. The parameters that trigger the test will be determined in the next Ethereum Foundation All-Core Developers call. These testnet merges, which served as sort of dress rehearsals for the real thing, each take developers one step closer to Ethereum's mainnet PoS upgrade.

Read more: Merge Testing on Ethereum: What Is It and Why Does It Matter?