This is the big one, it has been consistently delayed but things seem to be finally coming together for the Ethereum Merge! The largest change will be the transition for Proof-of-Work to Proof-of-Stake, which will set the stage for future scaling improvements, whilst also reducing the emission of new Ether by 90%.
Get technical about the Merge here
Checkout how price is responding here
Note: the date is not firm and has already been delayed many, many times!