Ethereum developers said they successfully created a copy of the blockchain – known as a “shadow fork” – to provide a testing environment ahead of a crucial upgrade known as the Shanghai hard fork.

The shadow fork occurred at 10:40 coordinated universal time (5:40 a.m. ET), according to Parithosh Jayathi, DevOps engineer at the Ethereum Foundation.

In the hours since the fork happened, there were some glitches with Ethereum's nodes that use Geth clients, according to Marius Van Der Wijden, a software developer at the Ethereum Foundation. A client is a software that is used by nodes that operate the blockchain, and Geth is Ethereum's most popular client.

In preparation for Shanghai, which will unlock staked ether (ETH) withdrawals, the protocol will be undergoing a series of test forks that copy the data from the main network (mainnet) to a testing environment.

A shadow fork is a smaller test fork that focuses on some of the changes that need to happen before Shanghai eventually occurs on the main protocol. Ethereum used several shadow forks for testing ahead of last year’s big shift to a proof-of-stake network, known as the Merge.

During this latest shadow fork, developers focused on creating a testing environment for staked ETH withdrawals as well as improvements to reduce gas costs.

This shadow fork brings the much anticipated Shanghai upgrade closer to the Ethereum mainnet, expected in March 2023. The public testnet for Shanghai will also go live in the coming days.