EIP-6953 documents all network upgrade activation mechanisms used in Ethereum's history. It covers block number triggers (PoW era), beacon chain epoch triggers, Terminal Total Difficulty for The Merge, and post-merge timestamp-based activation on both execution and consensus layers.
This informational EIP serves as the definitive reference for how Ethereum upgrades activate. Developers, researchers, and node operators can consult one document to understand the upgrade history and current mechanism, rather than piecing together information from multiple sources.
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.
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should assume that future upgrades use the mechanism described in the Post Merge Upgrades section, unless this EIP is superseded by another one.
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 |
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:
524288 ETH from 16384 validators.MIN_GENESIS_TIME timestamp of 1606824000 (Dec 1, 2020) had been exceeded.GENESIS_DELAY of 604800 seconds had passed since the minimum validator count was exceeded.Beacon Chain upgrades are activated at specific epochs. The following upgrades followed this pattern:
| Upgrade Name | Activation Epoch |
|---|---|
| Altair | 74240 |
| Bellatrix | 144896 |
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.
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 8192 slots). 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
Blocks and epochs serve as natural trigger points for upgrades, as they represent the levels at which state transitions occur on Ethereum.
For the Terminal Total Difficulty mechanism, the rationale can be found in EIP-3675.
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.
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