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ELI5 2023 Avalanche Cortina Update

On April 25 2023, Avalanche activated the Cortina update.

According to Ava Labs founder, Emin Gun Sirer, there are 3 major advancements in Cortina:

  1. X-Chain linearization
  2. Increased GAS limit for the C-Chain
  3. Batched delegator rewards

Let’s take a closer look at each!

X-Chain Linearization

As you problably know, the X-Chain (where the native AVAX gets transferred) used to be a DAG. A DAG is like a multi-dimensional blockchain, where several chains all head forward in the same direction. This is a very interesting concept, especially in a metastable consensus mechanism such as Avalanche. In this kind of system, each validator forms its own opinion about the validity transactions. So, several nodes could have several different DAG’s. The only thing they have in common is that the DAG branches always grow forward and meet up again at consensus.

This is a really cool structure, but it’s really complex to manage. Especially for exchanges, explorers and other applications.

For example, Avalanche X-Chain vertices do not have a unique timestamp. If validator A received and approved Tx1 at 10:01 AM and validator B received it at 10:02, both validators will have a copy of the validated Tx1 recorded at different times. So block explorers may each show a different timestamp for the same vertex. This is different from Bitcoin, Cardano and others where blocks will only have one timestamp that is the same across the entire network.

So, how does Cortina change this?

As you may have guessed, the DAG has now been turned into a single blockchain. Basically what was several blockchains running in parallel has now been reduced to a single linear chain. When you have a single chain, the vertices can only be assembled in one valid order. It really simplifies things.

Avalanche X-Chain now follows the classic definition of a blockchain, as used by Bitcoin, Cardano, Ethereum and others.

Its consensus engine has also changed, now all official chains use the Snowman++ consensus engine. It’s yet another improvement, where the software will be simplified, especially for high volume deployments like exchanges and popular block explorers.

Increased GAS Limit

The Avalanche C-Chain is where contracts live. By contracts, think Ethereum-compatible smart contracts. In fact, the C-Chain uses the Ethereum virtual machine for its implementation. (Avalanche can run any number of VM’s and subnets. You could plug Bitcoin and run it inside Avalanche on its own VM.)

Just like Ethereum, Avalanche uses a second abstraction to calculate transaction fees. This abstraction is called GAS and if you’ve ever transferred any assets on Avalanche C-Chain then you’ve already used GAS.

The maximum amount of GAS used to be 8 million per block. Cortina has almost doubled this limit to 18 million GAS. Avalanche C-Chain uses a 10 second block time, so every 10 seconds the network will accommodate a block with a maximum of 15 million GAS fee.

What does this mean?

The EVM (Ethereum Virtual Machine) used by the C-Chain charges its users by the amount of computing power spent. It’s a bit like a restaurant menu, with a price for each function.

A dAPP (decentralized app) will contain many functions inside it. When you interact with a dAPP using Metamask or Core Wallet, you’re actually sending commands to a smart contract that is hosted on the C-Chain. Each of those commands has a GAS price.

If you limit the amount of GAS on each C-Chain block, then you also limit how many functions the dAPP is able to run.

Since Avalanche is now hosting complex games and all sorts of web3 applications, the Avalanche team decided to increase the maximum GAS allowed per block. This will allow much more sophisticated code to be run on the already lightning fast Avalanche platform.

Batched Delegator Rewards

When your staked AVAX period ends, the protocol will generate a reward transaction for you. This works great from a delegator point of view.

But validators do a lot of work at every expired delegation. A validator node with 1000’s of delegators will have to issue one reward transaction for every delegator.

Cortina introduced batched rewards. Now validators will queue all delegator fee UTXO’s and issue just one large Tx at the end of its cycle.

With over 1250 active validators at the time of this writing, Avalanche is one of the most decentralized DeFi platforms available. Now, at the end of each of these validators’ cycles, there won’t be a tsunami of Tx’s for the network to process. One Tx per validator and all fees get settled.


The Avalanche Cortina update went live on April 25 at 11 AM Eastern Time. If you’re an avid Avalancher, you probably know that Avalanche always uses Eastern Time (that’s Cornell University’s time zone … just a coincidence wink wink).

The update went so smoothly, that nobody actually noticed. It was probably one of the most complex updates in cryptocurrency history, yet it was totally uneventful. A reward for the perfect engineering by the Avalanche developer team!

Here’s a link to the very first linear X-Chain block! From this point onwards, X-Chain is a single chain, C-Chain allows 15M GAS per block and delegator fee rewards are batched and submitted in a single Tx!


Cortina Update Thread by Avalanche Developers

Avalanche Activated the Important Cortina Upgrade on the Mainnet

Avalanche’s Cortina Upgrade Goes Live on Protocol’s Testnet; AVAX Token Rallies

Avalanche core team implements Cortina upgrade on mainnet

Cortina: X-Chain Linearization

About the Author
Published by Crypto Bill - Bill is a writer, geek, crypto-curious polyheurist, a dog's best friend and coffee addict. Information security expert, encryption software with interests in P2P networking, decentralized applications (dApps), smart contracts and crypto based payment solutions. Learn More About Us