Ethereum is making progress on its transition to proof of stake, known as The Merge. Development networks are being set up, specifications are being finalized, and the community is actively engaged. The goal is to ensure that The Merge has minimal impact on end users, smart contracts, and dapps. However, there are a few minor changes worth noting.
After The Merge, proof of work blocks will no longer exist on the Ethereum network. Instead, the contents of these blocks will become part of the blocks created on the Beacon Chain, which will serve as the new proof of stake consensus layer. These blocks on the Beacon Chain will contain ExecutionPayloads, equivalent to the current proof of work blocks. End users and application developers will interact with Ethereum through these ExecutionPayloads, which will still be processed by execution layer clients such as Besu, Erigon, Geth, and Nethermind. Thankfully, the stability of the execution layer means that The Merge will introduce minimal breaking changes.
With the transition to proof of stake, certain fields in the block headers that were relevant to proof of work will become unused. To minimize disruption, these fields will be set to 0 or their equivalent, rather than being completely removed. One example is the ommers field, which will be set to RLP-encoded hash of an empty list. Other changes include the modifications to the BLOCKHASH and DIFFICULTY opcodes, which will provide weaker pseudorandomness and a stronger source of randomness, respectively. These changes will be reflected in the ExecutionPayloads.
The Merge will also impact the average block time on Ethereum. Under proof of work, blocks come in every ~13 seconds with some variance. Under proof of stake, blocks will come in exactly every 12 seconds, except when a slot is missed. This will result in approximately a 1-second reduction in average block times. Smart contracts that rely on a particular average block time will need to account for this change.
Finally, after The Merge, the concepts of finalized blocks and safe head will replace the traditional notion of confirmed blocks in the execution layer. A finalized block is one that has been accepted as canonical by over two-thirds of validators, making it extremely difficult to create a conflicting block. A safe head block has been justified by the Beacon Chain, indicating that over two-thirds of validators have attested to it. These blocks can serve as a stronger substitute for proof of work confirmations and will be exposed through execution layer APIs.
To prepare for the transition to proof of stake, application developers can expect a long-lived testnet to be made available soon. Additionally, a Merge community call will provide an opportunity for developers to ask questions and receive updates on the technical aspects of The Merge.