Key facts:
Sepolia, after Rinkeby, is the second testnet to complete the merger.
The merger into the Ethereum mainnet is expected to take place later this year.
Sepolia, an Ethereum testnet, successfully completed the merger (“The Merge”) towards proof of stake. This is the second network to do so.
To block height 1,450,409 of the Sepolia network, the merge protocol was launched, which made the transition from proof of work (PoW) proof of stake (PoS).
According to Parithosh Jayanthi, one of the core developers of Ethereum, the merger in Sepolia was a complete success. However, there were a number of drawbacks in the configuration of the clients that affected 25% of the nodes. Jayanthi points out that these problems were solved without the need for interventionsince the protocol, by itself, achieved the solution.
Sepolia then becomes the second testnet to achieve the merger behind Rinkeby. But, it was the first long-standing testnet to be merged, as Rinkeby support will be withdrawn this coming December. Sepolia will live with the Ethereum 2.0 mainnet throughout its life cycle.
Testnets, such as Sepolia or Rinkeby, are protocols that simulate the operation of the mainnet, but are designed to run high-stakes tests on them. Only if they are successful are they then taken to the main network. If a serious testnet failure were to occur, it would not result in monetary loss for any Ethereum user.
After Sepolia, the next testnet to be merged will be Goerli, which, like Sepolia, will be a long-standing Ethereum 2.0 ecosystem.
About the merger or The Merge, is how the transition event between PoW and PoS is known. Upon execution, Ethereum ledger moves from a Proof-of-Work blockchain (Ethereum 1.0) to the Proof-of-Stake Ethereum 2.0 Beacon Chain. The merger on the Ethereum mainnet is expected to occur by the end of 2022.