What Is the Ethereum London Hard Fork? How EIP-1559 Changed Gas Fees?
The Ethereum London hard fork was a major network upgrade activated on August 5, 2021, at block 12,965,000, best known for introducing EIP-1559 to overhaul transaction fees. By implementing a protocol-calculated base fee that gets burned alongside an optional priority fee (tip) for validators, London made gas fee estimation more predictable and tied ETH token supply directly to network usage. The upgrade comprised five total EIPs that also reduced gas refunds, reserved EVM bytecode prefixes, and delayed the difficulty bomb to prepare Ethereum for its eventual transition to proof-of-stake.
The Ethereum London hard fork was a coordinated network upgrade activated at block 12,965,000 on August 5, 2021. It changed Ethereum's execution rules through five proposals, led by EIP-1559, which introduced a protocol-calculated base fee, an optional priority fee, variable block capacity, and the burning of the base-fee portion of every eligible transaction.
London addressed unstable fee estimation and several gas-accounting issues on Ethereum's former proof-of-work chain. It did not make transactions permanently cheap or turn Ethereum into proof of stake. Instead, it made the next block's base fee more predictable, changed how users bid for inclusion, reduced certain storage refunds, and delayed the difficulty bomb before the later Merge.
What Is the Ethereum London Hard Fork?
The Ethereum London hard fork was a major network upgrade that changed several execution-layer rules on Ethereum. Activated in August 2021, it introduced five Ethereum Improvement Proposals (EIPs), including EIP-1559, which redesigned the transaction-fee system and introduced the burning of Ethereum’s base fee. London upgraded the existing Ethereum network rather than creating a separate cryptocurrency.
Beyond transaction fees, London also made the base fee available to smart contracts, reduced certain gas refunds, reserved an EVM bytecode prefix for future changes, and delayed the proof-of-work difficulty bomb. These updates changed how wallets and applications interacted with Ethereum and prepared the network for later upgrades.
How Does the Ethereum London Hard Fork Work?
EIP-1559 changed gas fees by splitting the payment into a base fee set by the protocol and a priority fee offered to the block producer. Users specify a maximum total fee and a maximum priority fee. The transaction pays the current base fee plus an allowed tip, up to the user's maximum, and unused headroom is returned rather than paid automatically. The base fee is burned, while the priority fee compensates the block producer.
The base fee rises when the previous block uses more gas than the target and falls when usage is below the target. London also allowed blocks to expand up to twice the target gas usage during short demand spikes. This elasticity can absorb temporary congestion, but sustained demand still raises the base fee until demand matches available block space. London improved fee estimation; it did not impose a fixed low fee.
What Were the Main Changes and Use Cases of the London Upgrade?
London changed both user-facing fee behavior and lower-level execution rules. The five included proposals served different purposes, so reducing the upgrade to base-fee burning misses several operational changes.
1. EIP-1559 redesigned the fee market. Wallets gained a predictable protocol base fee, optional priority fee, maximum fee cap, elastic block capacity, and automatic burning of the base-fee payment.
2. EIP-3198 exposed the base fee to contracts. The BASEFEE opcode lets smart contracts read the current block's base fee, enabling on-chain logic that needs a protocol-defined gas-price reference.
3. EIP-3529 reduced gas refunds. The upgrade removed the SELFDESTRUCT refund and lowered the maximum refund, reducing incentives to maintain gas tokens or inflate blocks through refund-based strategies.
4. EIP-3541 reserved a bytecode prefix. New contracts beginning with 0xEF could no longer be deployed, preserving that prefix for a future EVM object format without invalidating existing contracts.
5. EIP-3554 delayed the difficulty bomb. The proposal postponed the rapid proof-of-work difficulty increase, giving developers more time before Ethereum's eventual transition to proof of stake.
What Are Examples of London's Impact on Ethereum?
London remains visible in ordinary Ethereum activity even though later upgrades changed consensus and expanded rollup scaling. Its fee fields and burn mechanism continue to shape wallets, blocks, and ETH supply accounting.
• Wallet fee estimates became easier to automate. Wallets can derive a likely base fee from recent blocks and add a priority fee instead of asking users to guess one all-inclusive gas price.
• Block capacity can respond to short spikes. A block may temporarily exceed the target gas usage up to the protocol limit, although continued congestion causes the base fee to increase.
• Every base-fee payment removes ETH from supply. The protocol burns the base-fee portion rather than awarding it to the validator, linking network usage to ETH destruction without guaranteeing deflation.
• Applications can reference BASEFEE on-chain. Contracts may use the opcode introduced by EIP-3198 when a calculation needs access to the current block's protocol-defined base fee.
What Are the Limitations and Risks of the London Upgrade?
London improved fee mechanics but did not eliminate scarcity in Ethereum block space. Users, wallet developers, and smart-contract developers still need to account for congestion, fee caps, variable execution costs, and the behavior of later network upgrades.
1. Gas fees can still become expensive. When demand remains above the target for consecutive blocks, the base fee keeps rising, so London improves predictability without guaranteeing affordability.
2. Incorrect fee caps can delay transactions. A maximum fee set below the future base fee prevents inclusion until fees fall, while an unnecessarily high tip can still overpay for priority.
3. ETH burning does not guarantee deflation. Net supply depends on how much ETH is issued compared with how much base fee is burned across network activity and the prevailing consensus rules.
4. Contract assumptions required review. Developers relying on historical gas refunds, transaction fields, or bytecode deployment patterns had to update their designs for the new execution rules.
Did the London Hard Fork Make Ethereum Deflationary?
The London hard fork did not make Ethereum permanently deflationary. It introduced a fee-burning mechanism that removes ETH whenever users pay the base fee, but net supply still depends on issuance and total burned fees. After Ethereum moved to proof of stake, issuance fell substantially, making periods of net supply contraction more possible. Network activity can still fall low enough for issuance to exceed burns.
Related Concepts
1. What Is Gas?
Further Reading
1. What Is Ethereum (ETH)? A Beginner’s Guide to How Ethereum Works (2026)
2. Ethereum Gas Fees Explained: What Is ETH Gas and How Does Gwei Work?
3. Ethereum's 10th Anniversary: Top 10 Milestones of the World’s Second‑Largest Blockchain
4. What Is the Ethereum Pectra Upgrade That Went Live on May 7, 2025?
5. Ethereum Fusaka Upgrade on December 3, 2025: What You Need to Know
6. What Is Ethereum Glamsterdam Upgrade in H1 2026 and What Changes Does the Hard Fork Bring?
FAQ
When did the Ethereum London hard fork happen?
London activated on Ethereum Mainnet at block 12,965,000 on August 5, 2021. Node operators had to run compatible client software to continue following the upgraded network rules.
Does Ethereum still use EIP-1559 after the Merge?
Who receives the priority fee after EIP-1559?
Why can a transaction remain pending after London?
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