The Ethereum network will be undergoing a scheduled upgrade at block number 13,773,000, which is predicted to occur on Wednesday, December 8, 2021. The exact date is subject to change due to variable block times and timezones. Please upgrade your node before Sunday, December 5, 2021 to account for the variable block times.

What is Arrow Glacier?

The Arrow Glacier network upgrade, similarly to Muir Glacier, changes the parameters of the Ice Age/Difficulty Bomb, pushing it back several months. This has also been done in the Byzantium, Constantinople and London network upgrades. No other changes are introduced as part of Arrow Glacier.

The difficulty bomb only affects Proof of Work networks, and hence only exists on the Ethereum mainnet and the Ropsten test network. With the recent progress towards Ethereum's transition to Proof of Stake, it was decided to only delay the bomb on mainnet for now and to try and run the Proof of Stake transition on Ropsten before the bomb goes off on that network.

To learn more about Arrow Glacier and the history of the difficulty bomb, see the Ethereum Cat Herders' explainer blog post.

Client Versions

In order to be compatible with the Arrow Glacier upgrade, node operators will need to update the client version that they run to one of the ones listed below:

Note: OpenEthereum, which was announced as deprecated earlier this year, has released support for Arrow Glacier under version number 3.3.0-rc.14, which you can download here.

For now, we still recommend following the prior deprecation warnings and selecting an alternative client software. If you choose to use OE for the Arrow Glacir upgrade, please exercise caution and independently review changes to the codebase prior to running in production.

Upgrade Specification and EIPs

The full specification for the upgrade can be found in the execution-specs repository here.

A single EIP is included in the upgrade: EIP-4345: Difficulty Bomb Delay to June 2022.

As an Ethereum user or ether holder is there anything I need to do?

If you use an exchange, a web wallet service, a mobile wallet service, or a hardware wallet you do not need to do anything unless you are informed to take additional steps by your exchange or wallet service.

As a node operator or miner, what do I need to do?

Download the latest version of your Ethereum client, as listed in the table above.

What happens if I am a miner or node operator and I do not participate in the upgrade?

If you are using an Ethereum client that is not updated to the latest version (listed above), your client will sync to the pre-fork blockchain once the upgrade occurs. You will be stuck on an incompatible chain following the old rules and you will be unable to send Ether or operate on the post-upgrade Ethereum network.

What is a network upgrade in Ethereum-land?

A network upgrade is a change to the underlying Ethereum protocol, creating new rules to improve the system. 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.

What happens during a network upgrade?

After the community comes to an agreement concerning which changes should be included in the upgrade, changes to the protocol are written into the various Ethereum clients, such as geth, Erigon, Besu and Nethermind. The protocol changes are activated at a specific block number. Any nodes that have not been upgraded to the new ruleset will be abandoned on the old chain where the previous rules continue to exist.

Why "Arrow Glacier"?

While we've recently been using Devcon names for network upgrades, when we previously had an upgrade that only pushed back the bomb, we decided to switch nomenclature. To highlight the nature of the upgrade (pushing back the "Ice Age"), we went with a glacier name, hence Muir Glacier.

This upgrade follows a similar pattern. Because the transition to Proof of Stake is on the horizon, a retreating glacier was chosen, hence Arrow Glacier 🏔!

Thank You!

A big thanks to the Ethereum community and to all Ethereum developers across all clients and platforms who come together to provide input, thoughts, and contributions. This might be the last network upgrade on Ethereum before the transition to Proof of Stake. Let's go!

Also, many thanks to Harshil Gudka for the cover image.

This is an emergent and evolving highly technical space. If you choose to implement the recommendations in this post and continue to participate, you should make sure you understand how it impacts you. You should understand that there are risks involved including but not limited to risks like unexpected bugs. By choosing to implement these recommendations, you alone assume the risks of the consequences. This post and recommendations are not a sale of any kind, and do not create any warranties of any kind including but not limited to anything related to the Ethereum network, or the Ethereum clients referred to herein.