Sepolia, a closed testnet for the Ethereum developers only, is the second such network to undergo the upgrade. Earlier this week, the Zhejiang testnet ran its own successful simulation of staked ETH withdrawals. There’s one more test network set to get the upgrade, and then the main Ethereum blockchain is expected to undergo the Shanghai hard fork next month.
The Sepolia testnet is closed to developers who run validators on the network. By contrast, Zhejiang is a public testnet, meaning that it was open to anyone, including staking providers, who wanted to practice the release of staked ETH.
After Sepolia goes through its own round of testing, Goerli will be the final testnet to get the Shanghai upgrade. Goerli will be the most anticipated test, given that it is the largest public Ethereum testnet, representing the last chance for staking providers to ensure that staked ETH withdrawals work before Shanghai goes live on the mainnet.
Barnabas Busa, a DevOps engineer at the Ethereum Foundation, told CoinDesk that the difference between the three tests comes down to “the number of visitors participating and network load.”
Shanghai will be the first hard fork for Ethereum since it went through the Merge in September, which switched out its old energy-intensive proof-of-work (PoW) model for a proof-of-stake (PoS) consensus mechanism. Under PoS, ETH is “staked” on the blockchain as a mechanism for helping to validate and secure transactions.