The fork called Istanbul has been successfully deployed on the Ethereum blockchain at block number 9069000.
This was announced by the co-founder of Ethereum Vitalik Buterin himself, revealing that the block was mined by Spark Pool.
Congrats to @sparkpool_eth for mining the Istanbul fork block!
— vitalik.eth (@VitalikButerin) December 8, 2019
Block number 9069000 was mined at 12:25:09 AM UTC on December 8th, 2019.
As stated by Kobi Gurkan, the new features introduced by Istanbul now make the verification cheaper, since a Groth16 verification costs about 200k of GAS (or 8k per input), as does PLONK.
This is the third update of the Ethereum protocol in 2019, after St. Petersburg and Constantinople. In total it is the eighth hard fork of the network and even this time all Ethereum clients have accepted it.
Istanbul included six improvement proposals, namely EIP 152, 1108, 1344, 1844, 2028 and 2200.
These updates changed the cost of some operations to prevent spam and improve overall resilience to denial-of-service attacks.
In addition, the new protocol allows greater interoperability with Zcash and other proof-of-work-based cryptocurrencies with the Equihash algorithm.
As far as Ethereum users are concerned, they do not have to do anything if they use services such as MetaMask or Coinbase Wallet, or if they hold funds on exchanges or hardware wallets, unless they have explicit requests from, for example, individual exchanges.
Node owners, on the other hand, must have their software updated with a client version compatible with the new protocol.
Despite some last-minute problems caused by an urgent patch being installed on Parity, the fork seems to have happened without major problems, also because the nodes had already updated the software before December 1st.
The new protocol has had an impact on some old smart contracts, which are no longer compatible and therefore have become obsolete, including 680 on Aragon which will be interrupted.
In addition, some changes have affected the way funds can be sent between DAOs, forcing users to manually migrate smart contracts.