Network Upgrade Activation Triggers

Abstract

This EIP outlines the various network upgrade activation triggers used on Ethereum over time, from the proof-of-work era to the first post-merge network upgrade, Shanghai/Capella, across both the execution and consensus layers.

Motivation

This EIP aims to provide users and developers with a single source of truth for understanding the various upgrade activation patterns used throughout Ethereum's history. It does not aim to be a comprehensive, ongoing record, of upgrades and their activations mechanism. Readers should assume that future upgrades use the mechanism described in the Post Merge Upgrades section, unless this EIP is superseded by another one.

Specification

Proof-of-Work Network Upgrades

During the proof-of-work era, network upgrades on Ethereum were triggered based on specific block numbers. The following upgrades followed this pattern:

Upgrade Name	Activation Block Number
Frontier	1
Frontier Thawing	200000
Homestead	1150000
DAO Fork	1920000
Tangerine Whistle	2463000
Spurious Dragon	2675000
Byzantium	4370000
Constantinople	7280000
Petersburg	7280000
Istanbul	9069000
Muir Glacier	9200000
Berlin	12244000
London	12965000
Arrow Glacier	13773000
Gray Glacier	15050000

Beacon Chain Launch

The Beacon Chain was launched following a set of conditions detailed in EIP-2982. The launch was activated once all the following conditions were met:

1. The Beacon Chain deposit contract received at least 524288 ETH from 16384 validators.
2. The MIN_GENESIS_TIME timestamp of 1606824000 (Dec 1, 2020) had been exceeded.
3. A GENESIS_DELAY of 604800 seconds had passed since the minimum validator count was exceeded.

Beacon Chain Upgrades

Beacon Chain upgrades are activated at specific epochs. The following upgrades followed this pattern:

Upgrade Name	Activation Epoch
Altair	74240
Bellatrix	144896

The Merge: Paris Upgrade

The Paris upgrade, the execution layer portion of "The Merge," was triggered by a proof-of-work Total Difficulty value of 58750000000000000000000, as specified in EIP-3675. Note that the activation of the Bellatrix upgrade on the Beacon Chain was a pre-requisite for the Paris upgrade to successfully activate on the proof-of-work chain.

Post-Merge Upgrades

After The Merge, network upgrades are triggered at an epoch on the consensus layer (CL), which ideally maps to an historical roots accumulator boundary (i.e., a multiple of 7192 epochs). The epoch's corresponding timestamp, rather than a block number, is then used on the execution layer (EL) as the activation trigger. The following upgrades followed this pattern:

Upgrade Name	Activation Epoch	Activation Timestamp
Capella (CL)	194048
Shanghai (EL)		1681338455

Note that epoch 194048 happened at timestamp 1681338455. In other words, the upgrades activated simultaneously on both the execution and consensus layers, even though they each used a different constant to trigger it.

Additionally, the use of timestamps on the execution layer resulted in changes to how nodes' FORK_HASH and FORK_NEXT values are calculated. These are described in EIP-6122

Rationale

Blocks and Epochs

Blocks and epochs serve as natural trigger points for upgrades, as they represent the levels at which state transitions occur on Ethereum.

Terminal Total Difficulty

For the Terminal Total Difficulty mechanism, the rationale can be found in EIP-3675.

Timestamps

Due to the possibility of missed slots on the Beacon Chain, the execution layer cannot rely solely on block numbers to trigger upgrades in sync with the consensus layer.

Timestamps are guaranteed to map to a specific epoch, and in their Unix representation, timestamps will always be greater than the block numbers previously used. This allows for a reliable method to trigger upgrades on the execution layer post-merge, while also ensuring that a post-merge upgrade based on a timestamp can never use a value that is considered lower than the last block-triggered upgrade.

Security Considerations

None.

Copyright

Copyright and related rights waived via CC0.