Ethereum is the first and most successful smart contract platform in the world. In order to maintain that status, its blockchain is under constant development for improvements and has changed over the years. If an upgrade is going to change the fundamentals of a blockchain it is usually implemented with a so-called hard fork.

Ethereum’s journey started in the year 2013 with its whitepaper and continued with long series of hard forks, each being a milestone that was extending the boundaries of its blockchain. In this article, we are going to explore the history of these many forks and what has been achieved so far.

Pre-Release: Olympic

Olympic was a pre-release of Ethereum that was announced on May 9th, 2015, by the Ethereum Foundation. The basic idea was to open up for developers and establish a bounty program to weed out any bugs and provide an incentive for miners to start connecting to the network and try things out.

The network only lasted for 14 days and technically Olympic wasn’t a hard fork but a completely different network. Still, it is worth mentioning since it played an important role in the Frontier release which created the Genesis block of Ethereum.

Genesis: Frontier and Frontier thawing

Frontier was the official release of Ethereum 1.0 including a genesis block that included 8893 transactions of all participants in the initial token sale that was concluded one year earlier. A total of a little bit more than 72 million Ether was created. Around 12 million ETH were allocated to the Ethereum development found.

Initially, Ethereum had a hardcoded gas limit of 5.000 gas per block. Since every transaction had a base fee of 21.000 gas, Ethereum was basically running in a mining-only mode at that time. Frontier thawing increased this limit and the first actual transaction was possible at block #46,147.

Homestead with three proposals

Homestead was a hard fork that included three Ethereum Improvement Proposals or in short EIPs:

• EIP 2: Homestead hard-fork changes
• EIP 7: Hardfork EVM update: DELEGATECALL
• EIP 8: Forward compatibility requirements for homestead

The DAO fork

The DAO fork is one of the most notable incidents in Ethereum history. It marked the birth of the Ethereum Classic blockchain. It was a response to a hack that happened in 2016 and caused a chain re-org effectively setting the blockchain back to a point before the hack has happened.

The hard fork caused quite a controversy since many people believed that all transactions – even those malicious – should be final. Ethereum Classic kept the balances and continued the chain with the hacker still in possession of his tokens.

Tangerine whistle

This hard fork addressed a problem caused by denial of service attacks (DoS) on the network. It was an urgent response to maintain the network’s health and address issues of underpriced operation codes that made it cheap to create spam.

Spurious Dragon

This fork was the second step to address the problems with DoS attacks on the network and it included:

• Opcode pricing to prevent future attacks
• Enabling debloat
• Replay attack protection

Byzantium

This fork added several changes that were crucial for the network:

• Reducing the mining rewards from 5 ETH to 3 ETH
• Delayed the difficulty bomb by a year
• Non-state-changing calls to other contracts
• Cryptography methods to allow layer 2 scaling

Delaying the difficulty bomb is a step that was undertaken for the first time. The bomb was created as an element to move on to proof of stake by making it so difficult for miners to find a new block so that they would have to quit their operations and support the new consensus mechanism.

Constantinople and St. Petersburg

These two forks marked the second half of the so-called metropolis stage. Only 32 hours before Constantinople was rolled out a serious problem was discovered and the hard fork was postponed. The changes that were meant to be made with Constantinople were undertaken by St. Petersburg which followed shortly after the delay.

• EIP 145: Optimised costs of on-chain actions
• EIP 1014: Interaction with addresses that haven’t been created
• EIP 1052: EXTCODEHASH opcode
• EIP 1234: Constantinople Difficulty Bomb Delay and Block Reward Adjustment

Instanbul

The fork was commenced in December 2019 and included:

• Optimized gas cost in the EVM
• Improved layer2 scaling solutions
• Enabled Zcash and Ethereum to interoperate

Muir Glacier

This hard fork delayed the difficulty bomb another time in January 2020.

Beacon Chain Genesis

The Beacon chain was introduced with two forks. The first one deployed staking deposit contracts in October 2020 followed by the Genesis event in December 2020. The start of the beacon chain was effectively the start of Ethereum staking and the transition to Ethereum 2.0

Ethereum hard forks in 2021

A more recent hard fork was Berlin in April 2021 introducing an upgrade to optimize gas costs for certain EVM transactions and better support of multiple transaction types. The London hard fork came 4 months later in August 2021 and introduced EIP 1559.

This upgrade introduces a fee market and the burning of fees, which could potentially transform Ethereum into a deflationary asset. If the demand exceeds the emission, the total emission rate goes negative.

Altair was the first upgrade for the beacon chain in October 2021. It enabled light clients and brought slashing penalties up to their full values.

The last one in December 2021 was Arrow Glacier. Again the only purpose was to delay the difficulty bomb but this time until June 2022.

Also read: The Ethereum Roadmap for the years ahead