The long-anticipated upgrade Constantinople has officially activated on the ethereum blockchain.

At 19:57 (UTC), the sixth system-wide upgrade to be released since the second largest cryptocurrency by market cap launched in 2015 has successfully been rolled out onto the main network at block number 7,280,000.

But, that’s not all. The unusual part about today’s hard fork is that are two of them. St. Petersburg – ethereum’s seventh system-wide upgrade – has been released simultaneously and as intended has disabled part of the Constantinople code deemed back in January to host security vulnerabilities that could be used by attackers to steal funds.

It’s such a big upgrade, it’s important it goes well so as to not cause ethereum to split. So far, as seen on blockchain monitoring website Fork Monitor, there is no evidence of a significant chain split to suggest a portion of ethereum users are still running on old ethereum software.

As background, before any system-wide upgrade also called a hard fork, users such as miners and operators of ethereum-based applications are required to install new client software that automatically updates at the exact same block number.

This prevents two concurrent and incompatible versions of the same blockchain from splitting the wider network.

“With the blockchain, everyone has to upgrade in order for everyone to be able to use [the new] features,” explained Taylor Monahan – CEO of blockchain wallet tool MyCrypto.

That means everyone has to be prepared ahead of time.

“About two weeks before the fork, everyone upgrades the software but none of the new features are enabled,” said Monahan to CoinDesk. “Then, on that block number, everyone at the exact same time starts using the new features. So, that’s how we prevent differing states from existing simultaneously. It’s [also] called a consensus issue or a consensus bug.”

MyCrypto presently runs 10 to 15 computer servers also called nodes all running on the most updated version of the Parity ethereum client.

With today’s release of Constantinople and St. Petersberg, four different ethereum improvement proposals (EIPs) have been officially activated on the ethereum network – one of which does introduce a new “corner case” affecting smart contract immutability.

As of press time, the market price for ether – the main cryptocurrency of the network – has seen a small jump from $135.14 shortly prior to mainnet release and presently sits at $136.99, according to the CoinDesk Price Index.

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