The hotly anticipated “London” Ethereum hard fork now has a set block height for three testnets — a key penultimate step toward a full mainnet launch.

In a blog post on the Ethereum Foundation’s website, Ethereum core developer Tim Beiko wrote that the Ropsten, Goerli and Rinkeby testnets now have set block heights at which London will go live, with Ropsten expected to be the first at block 10,499,401, or sometime on June 24. Goerli is expected to be next on June 30, and Rinkeby on July 7.

A release schedule for the all-important mainnet upgrade is still being determined, however.

“As of now, only the testnets (Ropsten, Goerli, Rinkeby) have been scheduled for London. Once the upgrade has successfully been activated on these networks, a block will be set for the Ethereum mainnet and be communicated on this blog and in other venues,” Beiko wrote.

The London hard fork upgrade includes five Ethereum Improvement Proposal (EIP) upgrades, but the star of the show is EIP-1559. An overhaul of Ethereum’s existing fee structure, while developers note that EIP-1559 is not explicitly designed to reduce gas costs, many expected it to bring them down for users significantly. It may also cut into miner revenues by upward of 50%, however, which has led to some grublings about a “miner revolt” that has largely failed to materialize.

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The upgrade is considered to be one of many bullish catalysts on the horizon for Ethereum, not least of which is the Ethereum 2.0 upgrade. Eth2 will transition the network to a more environmentally-friendly proof-of-stake consensus mechanism, which will significantly decrease the energy consumption of validating blocks.

The blog post noted that such significant system upgrades to a decentralized system is a feat of coordination.

“The decentralized nature of blockchain systems makes a network upgrade more difficult. Network upgrades in a blockchain require cooperation and communication with the community, as well as with the developers of the various Ethereum clients in order for the transition to go smoothly.”