Ethereum's Proof-of-Stake Transition to Begin September 6th.
September 6th will be the starting date for the system-wide transition known as the merge.
The Merge refers to the switchover of Ethereum from proof-of-work to proof-of-stake.
According to calculations by the Ethereum Foundation, the new proof-of-stake method will use far less energy – 99.95 percent less.
Merge is a two step process - September 6 is only the first step.
The first step is the aforementioned Bellatrix upgrade, which is due to go live on September 6th at 11:34:47 AM UTC.
Once it goes live it starts another counter towards the TTD threshold.
TTD is essentially a measure of activity on the Ethereum network.
Once this limit is reached, another upgrade, paris, will be triggered and the merge will be completed.