On October 17th (block 4,370,000), Ethereum will hard fork to Byzantium, the first half of the larger Metropolis update. Unlike the Bitcoin hard fork, the Byzantium update is not expected to create another Ethereum coin. Although this update doesn’t introduce the much anticipated anonymous transactions and proof of stake, there are still some interesting changes to be aware of.
The mining reward will be reduced from 5 ETH to 3 ETH. This change is made in preparation for proof of stake, where mining will be phased out all together. Although the reward was reduced, the previous plan to exponentially increase block times (the ice age) has been delayed. The ice age was originally put in place to incentivize the adoption of new chains when hard forks are introduced.
Four native contracts have been added that allow for certain computationally expensive operations to be executed directly on the CPU that the Ethereum virtual machine runs on. These four functions (big mod exponentiation, elliptic curve addition, elliptic curve scalar multiplication, and elliptic curve pairing) are crucial to the implementation of zk-snarks, the cryptography that will one day allow for private transactions.