Ethereum (ETH) has launched its first pre-release for phase zero of the network’s evolving transition to Ethereum 2.0, according to new post published to Ethereum’s github on Jan. 31.

The post notes that “this marks the first release in a series of weekly releases through February 2019. Phase 0 in v0.1 is relatively feature complete and approaching stable.”

Ethereum 2.0, also known as Serenity, is planned to be the system’s final upgrade, as the entire network transitions from a proof-of-work (PoW) to a proof-of-stake (PoS) consensus algorithm, and tackles fundamental questions such as scalability, economic finality and security.

Serenity thus represents the last in a series of four stages set out in the platform’s roadmap; at present, the network is in its third stage (Metropolis) that consists of two system-wide hard forks— Byzantium and Constantinople — both designed to pave the way to Ethereum 2.0. The latter was notably recently delayed due to a vulnerability issue detected mid-January.

Commenting on today’s first pre-release for Serenity, Ethereum co-founder Vitalik suggested it was “*baaasically* feature complete for Casper.” As reported, Casper FFG — which stands for Casper the Friendly Finality Gadget — was first published in October 2017, as a PoS-PoW hybrid consensus model designed to provide stronger economic finality and security.

Other PoS solutions planned for Ethereum 2.0 notably include the sharding scalability feature — which split ups transaction processing between smaller groups of nodes to increase the blockchain's total throughput.

Alongside Ethereum 2.0’s first pre-release, a new testnet — dubbed “Gorli” — went live yesterday, and will serve to trial a key sharding client for Serenity, known as Prysm.

For developers, a testnet provides a simulated version of the primary network that allows them to try out smart contracts or upgrades without having to pay “gas” (computation fees) for their execution.

Gorli — an open-source, community-built initiative — will reportedly be instrumental in synching other major Ethereum clients such as Parity, Geth, Nethermind, Pantheon and EthereumJS.

As reported, the vulnerability that was found in the Constantinople hard fork last month was one that could have allowed for reentrancy attacks via the use of certain commands in ETH smart contracts. The critical issue was first detected by smart contract audit firm ChainSecurity.