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ETH2.0: The Altair Upgrade

October 28th, 2021

The beacon chain has been running soundly ever since launching late 2020 and had its very first upgrade on the Ethereum network this week at epoch 74240, or approximately 11am UTC on October 27th.

To accommodate developers with the upcoming “merge” — the event during which the Ethereum blockchain as we know it will transition to proof-of-stake — the Altair upgrade provides a few technical upgrades to make sure all is ready to go once Ethereum moves towards becoming its own shard on the network.

If you’d like a quick refresher on the changes ETH2 brings, what the beacon chain does, or what the merging event is all about, feel free to take a look at our previous ETH2 articles.

What’s New with Altair?

The Altair upgrade presents a “warm-up upgrade” in anticipation of the merge event, and will include some changes to ensure a smooth transition.

Light Clients

In order to make Ethereum as decentralized as possible and easily usable by anyone, it’s important that there’s no high degree of hardware requirements for getting started.

Right now, Ethereum clients have support for so-called light clients. These clients, or nodes, connect to other clients on the network that store the full history of the network (known as full nodes). This allows the light clients to interact with the network without having to download the entirety of Ethereum by themselves. By just storing the header of the network and only requesting data from full nodes whenever needed, light clients are able to do all the things a full node can while running on low-power machines.


The Altair upgrade introduces support for “sync committees” to the beacon chain, which will enable light clients to easily sync up without setting high requirements regarding processing power or data usage. With the Altair upgrade laying down the initials of light client support for the beacon chain, it will ultimately be possible to run validator clients on low-power devices, such as mobile phones or browsers.

Updated Penalty Parameters

The beacon chain was initially launched with reduced penalties to encourage users to participate and become validators on the network. Since the chain has operated without major issues since launch, and has successfully slashed any validators’ funds who aren’t actively participating or who are performing malicious behaviour, it’s been decided that the penalty parameters will be increased according to the values initially set out in the ETH2 protocol.

The hash-slinging slasher

Inactive validators who stopped actively participating by no longer processing transactions or proposing new blocks will face a stronger penalty, causing them to lose their staked ETH more quickly.

Secondly, the minimum slashing penalty for validators who perform fraudulent actions on the network will be increased from 0.25 ETH to 0.5 ETH.

If you’re curious about the full technical details of this upgrade, you can find an annotated version of the Altair beacon chain spec here.


While you won’t be experiencing much of the ETH2 goodness we’re all looking forward to just yet, this update introduces a few improvements to make sure all is ready before the rest of ETH2 comes together and the merge commences.

To encourage developers to make sure everything surrounding this upgrade goes smoothly, the Ethereum Foundation is temporarily doubling its bug bounties for four weeks after the launch of Altair. Get involved here.

If you are running a validator client, you will have to update to the latest version of whichever client you might be using. In the case you don’t update your client, it won’t be compatible with the network and you will face penalties to your staked Ether.

Further Reading

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