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Date of last update: August 18, 2022

The Merge

The Merge is an Ethereum upgrade that merges the Beacon Chain into Ethereum Mainnet, turning Mainnet into a combination of an execution layer and consensus layer. The Merge transitions Mainnet from proof of work to proof of stake consensus.

Update and configure Besu to be ready for The Merge. You can also run Besu with a consensus client such as Teku on the Merge testnet.

Execution and consensus clients

After The Merge, a full Ethereum Mainnet node will be a combination of an execution client (previously called an Ethereum 1.0 client) and a consensus client (previously called an Ethereum 2.0 client).

Execution and consensus clients communicate with each other using the Engine API.

Ethereum Merge node

Execution clients

Execution clients, such as Besu, manage the execution layer, including executing transactions and updating the world state. Execution clients serve JSON-RPC API requests and communicate with each other in a peer-to-peer network.

Consensus clients

Consensus clients, such as Teku, contain beacon node and validator client implementations. The beacon node is the primary link to the Beacon Chain (consensus layer). The validator client performs validator duties on the consensus layer. Consensus clients serve REST API requests and communicate with each other in a peer-to-peer network.

What happens during The Merge

Before The Merge, the execution and consensus clients’ configurations will be updated to listen for a certain total terminal difficulty (TTD) to be reached.


The TTD is a specific value for the total difficulty, which is the sum of the proof-of-work mining difficulty for all blocks up to some point in the blockchain.

The consensus layer will enable the Merge configuration (Bellatrix) before reaching the TTD. Once the execution layer blocks reach the TTD, the Beacon Chain will merge into Ethereum Mainnet, and Ethereum will move to a proof of stake network.

After The Merge, a Mainnet node operator must run both an execution client and a beacon node at the same time. To become a validator, you must also run a validator client (either in the same process as the beacon node or separately.

After The Merge, validators earn rewards for performing validator duties, and fee recipients will also earn rewards for the inclusion of execution layer transactions.

Update and configure Besu to be ready for The Merge.