What is the Bellatrix Hard Fork: Ethereum’s Last Upgrade Before the Merge

Ethereum is on the precipice of transitioning to a Proof-of-Stake (PoS) consensus algorithm, and the Bellatrix hard fork is the last major upgrade before the actual Merge takes place.

Bellatrix is taking place today, September 6th, scheduled for epoch 144896 on the Beacon Chain. Here’s everything you need to know about it.

TLDR:

• The Merge is a “two-step” process.
• The first step is the Bellatrix hard fork triggered by an epoch height.
• The second step is the Paris upgrade, triggered by the TTD threshold.

A Short Introduction

Before diving into the specifics of the Bellatrix upgrade, it’s important to know its place in the overall roadmap toward the Merge.

As explained in our detailed guide on the Merge, this event is monumental in Ethereum’s history and perhaps even in the entire industry as a whole. It marks the first-ever transition of a large-scale network from a Proof-of-Work (PoW) consensus to Proof-of-Stake (PoS) and will drastically change issuance and operational specifics.

Even though the Merge will happen soon (barring unforeseen circumstances), it is the result of many years of research, development, and testing. It also happens following multiple upgrades that prepare the Ethereum network for it, and this is where Bellatrix comes into play.

What is the Bellatrix Hard Fork?

Bellatrix is the very last upgrade that Ethereum’s Beacon Chain will go through before it merges with the mainnet later in September.

Presently, each Ethereum node is represented on two different layers – the proof-of-work layer (currently the main network) and the consensus layer (C layer). The Merge entails that these two layers will be combined in a transition to a PoS-based system.

These layers communicate through an Application Programming Interface engine. The purpose of the Bellatrix upgrade is to enable validators to start producing updated Beacon Blocks, which will then contain the codebase for the merging of the two layers.

Tweeting on the matter was Vitalik Buterin, who said:

The merge is still expected to happen around Sep 13-15. What’s happening today is the Bellatrix hard fork, which *prepares* the chain for the merge. Still important though – make sure to update your clients!

Updating and syncing clients is critical to the upgrade, and at the time of this writing, almost 73% of the nodes appear to be “merge-ready.”

Core Ethereum developer Tim Beiko also pushed the remaining node operators to update their clients.

What’s Next?

After Bellatrix, the Merge is scheduled to take place in the so-called “Paris” upgrade. It’s the execution layer’s portion of the transition, and it will be triggered by Terminal Total Difficulty (TTD) of 58750000000000000000000. This is expected to take place between Sept 13th-15th. 

Once the execution layer reaches this TTD or exceeds it, the subsequent block will be produced by a validator on the Beacon Chain.

The Merge itself will be considered complete as soon as the Beacon Chain finalizes this particular block. If nothing out of the ordinary takes place, this will happen approximately 13 minutes (or 2 epochs) after the first post-TTD block is produced.

This is an overall image of what the entire process looks like: