The long awaited 'Byzantium' upgrade to the Ethereum network is announced for testnet deployment on September 18th. Dubbed as the 'next critical step' for Ethereum, it is the first of two substantial phases scheduled for the platform in this year's Metropolis update. The test phase will last several weeks before broader updates to the entire network are likely to take place starting sometime in October.
The second phase, called 'Constantinople', will be released later this year. It begins the shift towards Proof of Stake (PoS) for Ethereum, a major change from the current GPU mining Proof of Work technique for verifying transactions on the blockchain.
https://www.coindesk.com/metropolis-ahead-ethereum-developers-set-september-date-testnet-launch/
Read more about ETH Proof of Stake here: https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQ