Ethereum has successfully completed the Istanbul hard fork.

Hitting at block number 9,069,000, the systemwide upgrade is the network’s third in 2019, following February’s St. Petersburg and Constantinople hard forks. The months-long process culminated at 0:25 UTC on Sunday.

Another iteration of Ethereum 1.x, Istanbul is the network’s eighth hard fork overall with the first code changes being approved in June 2019. (Eth 2, the network’s major transition to proof-of-stake (PoS), is expected in 2021.) Being non-contentious, all ethereum clients – which host and independently upgrade the ethereum protocol themselves – have agreed to the new software. 

Istanbul includes six Ethereum Improvement Proposals (EIPs), specific code changes to the ethereum protocol, including EIPs 152, 1108, 1344, 1844, 2028 and 2200. 

According to a blog post from ethereum venture studio ConsenSys, the main issues addressed by the six EIPs are:

Stepping back, the cost to send a transaction on the ethereum network is called gas and paid in fractions of ETH called gwei. The lowered gas costs enabled by Istanbul’s EIPs are meant to increase bandwidth on the blockchain and foster zero-knowledge privacy technologies such as zk-SNARKs.

One scare before Istanbul took place was with ethereum client Parity, which released an urgent message to Parity Ethereum users to conduct a patch on the pre-released Parity Ethereum update before the Istanbul hard fork occurred. In short, EIP 1344 – concerning opcodes – was not initially included.

While the fix itself was simple, ethereum core developer Hudson Jameson said in the “AllCoreDevs” Gitter messaging platform that if Parity clients failed to update in time, a new chain could develop causing double spends.

“Parity represents about 23% of the network and is commonly used by major miners and exchanges,” Jameson said Friday. “I fear if one to two major exchanges stay on the old fork and one to two major mining pools mine the old chain it will cause confusion and in a more severe case double spends.”

As CoinDesk reported in September, 680 smart contracts on Aragon, a governance platform, will be broken by the planned hard fork.

Certain code changes will change how funds can be sent between decentralized autonomous organizations (DAOs), forcing users to manually migrate smart contracts from one structure to the other. 

While Aragon supports the continuing growth of ethereum, Aragon One CTO Jorge Izquierdo said ethereum developers need to be more cognizant of those developing on the network.

“Developers don’t want to build on a moving target, and backwards compatibility should be taken seriously as well,” Izquierdo said in an email to CoinDesk Friday. “Ethereum is not a toy anymore, it’s a platform with a sizable investment and a big reach, and as such changes like this need to be professionally measured before being taken.”