The Ethereum Merge: What Changes After the Execution Layer and Consensus Layer Combine

The Ethereum network is undergoing its most significant upgrade yet: the Merge. This transition moves the blockchain from a Proof-of-Work (PoW) consensus mechanism to a Proof-of-Stake (PoS) system. To prepare for this shift, the Ethereum Foundation has retired the terms "Eth1" and "Eth2." Instead, we now refer to the execution layer (formerly Eth1) and the consensus layer (formerly Eth2). Together, these layers form the new, upgraded Ethereum.

This upgrade has been in development for years and is now in its final public testing phase. The entire community—from core developers to everyday users—is eagerly anticipating a smooth transition that maintains network uptime, secures billions in assets, and supports thousands of nodes without disruption.

How the Merge Is Triggered

The Merge is activated by a specific technical condition on the Beacon Chain (the consensus layer). It continuously monitors the total difficulty of the current Ethereum PoW chain. Once this value meets or exceeds a predetermined threshold known as TERMINAL_TOTAL_DIFFICULTY, the next block produced will be the final PoW block. After that, all new blocks will be created and validated by the Beacon Chain using PoS.

This trigger mechanism ensures a deterministic and predictable shift between consensus models, minimizing potential risks or chain splits.

Expected Timeline for the Merge

Development work for the Merge is largely complete. Current estimates suggest the event will occur in the second quarter of 2022, most likely by June. However, this timeline depends on successful public testing. If critical bugs are discovered, the date may be pushed back.

The June target is tied to the Arrow Glacier upgrade implemented in December 2021, which included EIP-4345. This proposal delayed the "difficulty bomb"—a mechanism designed to gradually make PoW mining harder—until June 2022. If the Merge isn’t ready by then, the bomb would need to be delayed again to avoid disrupting the network before the transition.

Ethereum’s New Two-Layer Architecture

After the Merge, Ethereum will operate as a unified system comprising two main components:

• Execution Layer: Handles transaction execution, smart contract deployment, and state management.
• Consensus Layer: Manages block validation, committee consensus, and PoS mechanics via the Beacon Chain.

These layers, while integrated, remain structurally distinct:

• Each layer operates its own node software and peer-to-peer network.
• Each exposes its own API for developers and users.
• They communicate through a dedicated Engine API, which enables seamless coordination between execution and consensus tasks.

This design ensures backward compatibility for developers and users while introducing the scalability and security benefits of PoS.

Key Changes to the Execution Layer

The execution layer will see several important modifications once PoW is deprecated.

Block Structure Updates

Fields related to PoW mining will become obsolete and be set to zero or deprecated. These include:

• nonce
• mixHash
• difficulty
• ommers (uncle blocks)

Additionally, the extraData field will be limited to a maximum of 32 bytes.

Block validation logic will also be updated:

• Difficulty checks are removed.
• Nonce and mixHash validation are discontinued.
• Uncle block validation is eliminated.

Ether Issuance and Fee Mechanics

With the shift to PoS, block rewards for uncles cease entirely. However, the execution layer will continue processing transaction fees. These fees will be directed to the feeRecipient address specified in the ExecutionPayload.

Block Propagation

After the Merge, the execution layer will no longer broadcast new blocks. Clients will disable related message handlers such as NewBlockHashes (0x01) and NewBlock (0x07). The execution layer will still sync network state, broadcast transactions, and maintain the transaction mempool.

Introduction of the Engine API

The Engine API is a new set of endpoints exposed by the execution layer, separate from the standard JSON-RPC API. It runs on a different port and facilitates communication with the consensus layer.

Three key methods are introduced:

1. engine_newPayload: Validates an ExecutionPayload received from the consensus layer. Possible responses include VALID, INVALID, SYNCING, ACCEPTED, INVALID_BLOCK_HASH, and INVALID_TERMINAL_BLOCK.
2. engine_forkchoiceUpdated: Signals the execution layer to begin building a new block based on the latest fork choice data.
3. engine_getPayload: Retrieves the execution payload for a given payload ID, allowing the consensus layer to obtain block data for proposed new blocks.

These methods ensure that the two layers can coordinate block production and validation in real-time.

The Role of the Beacon Chain After the Merge

The Beacon Chain has been live since December 1, 2020, but until the Merge, it has been processing "empty" blocks without real transactions. After the Merge, it becomes the full consensus engine for Ethereum.

Block Production Workflow

When a new block is proposed in the PoS system, the following sequence occurs:

1. The consensus layer calls engine_forkchoiceUpdated on the execution layer, including payloadAttributes. The execution layer returns a payloadId.
2. The consensus layer uses engine_getPayload with that payloadId to retrieve the ExecutionPayload.
3. The consensus layer submits the payload to engine_newPayload for validation.
4. Finally, the consensus layer invokes engine_forkchoiceUpdated again to confirm the new head of the chain.

This workflow ensures that both layers agree on the validity and ordering of transactions and blocks.

Frequently Asked Questions

What is the difference between the execution layer and the consensus layer?
The execution layer handles transaction execution, smart contracts, and account balances. The consensus layer manages block validation, attestations, and the Proof-of-Stake mechanism. Together, they allow Ethereum to function securely without mining.

Will my existing ETH tokens or smart contracts be affected?
No. The Merge is a consensus-layer upgrade. All contracts, tokens, and user balances will remain intact and fully functional. No action is required from users or developers.

How will transaction fees change after the Merge?
Transaction fees will continue to be paid in ETH and will be directed to the validator instead of a miner. Fee mechanics remain the same from a user perspective.

What happens to miners after Ethereum moves to Proof-of-Stake?
Miners will no longer be needed for block production. Ethereum will rely on validators who stake ETH to secure the network. Miners may transition to other PoW networks or become stakers in the new system.

Can I run a node after the Merge?
Yes, but you will need to run both consensus and execution layer clients. 👉 Learn how to set up a complete node

Will the Merge reduce Ethereum’s energy consumption?
Yes. Moving from Proof-of-Work to Proof-of-Stake is expected to reduce Ethereum’s energy usage by over 99%.

The Merge marks a historic milestone for Ethereum—enhancing scalability, security, and sustainability while preserving the network’s decentralized nature. As the community prepares for this upgrade, understanding these technical changes helps users and developers navigate the new landscape with confidence.