Ethereum developers have postponed the Glamsterdam hard fork — a network-wide protocol upgrade that requires every node operator to update their client software — on the Hoodi testnet after security experts identified potential gas-accounting adjustments that could affect the functioning of currently deployed smart contracts during failed transactions.

The latest update pushes Ethereum's upcoming mainnet hard fork activation back indefinitely and casts doubt on the network's tentative December rollout window.

Glamsterdam timeline in doubt

In a blog post published on Thursday, the Ethereum Foundation said the activation was delayed due to security concerns. According to the Foundation, developers made a joint decision to postpone the update during the ACDE #248 call — the biweekly All Core Developers Execution meeting — in order to evaluate the interaction between the EIP-8037 proposal and the smart contracts currently deployed on the Ethereum mainnet.

Initially, the Hoodi hard fork was set to be activated on October 26 at 17:42:48 UTC at epoch 132,352, a fixed-length unit of time on Ethereum's consensus layer. That epoch has now been removed from the deployment configuration, without any new epoch being scheduled in its place. No replacement activation date was announced.

The delay also affects the deployment of the Gloas consensus-layer activation and a planned increase of Hoodi's current gas limit to 200 million — the ceiling on how much computation each block can carry — both of which form part of the Glamsterdam hard fork update package. The Foundation emphasized, however, that the schedule change will not affect Hoodi's existing chain history.

How the gas changes could backfire

The issue goes back to October 13, when blockchain auditing company ChainSecurity marked two Ethereum Improvement Proposals from the Glamsterdam upgrade — EIP-8037 and EIP-8038 — as a threat to current measures designed to prevent what it calls “insufficient gas griefing.” As per the attack, the caller deliberately sends insufficient gas so that a legitimate contract function fails.

Gas is the unit in which Ethereum meters computation, and contracts are written on the assumption that gas allocated to an operation is spent rather than returned. With the introduction of these measures, it would become possible to return gas to a contract once an operation fails, thus allowing further operation which would otherwise have stopped. Many contracts use the amount of gas remaining mid-transaction as one of their security measures. Altering that assumption would make it possible for a contract to finalize the failed operation, making it impossible for a user to claim anything or perform another operation.

The upgrade's scope extends beyond gas accounting. In a September 26 post on X, Ethereum co-founder Vitalik Buterin highlighted the sync improvements the upgrade is expected to bring:

Reminder: you can now sync an ethereum node within half a day and with aggressive settings the space it takes up on disk can be under half a terabyte. EIP-4444 and hard work by client teams on optimizing snap sync has improved things a lot. Glamsterdam will improve the sync situation further still (eg. Nimbus's new sync protocol uses it) — vitalik.eth (@VitalikButerin), September 26, 2026, on X

Some gas checks will withstand the changes regardless, but they will need to be audited against Glamsterdam's new accounting system.

13 real-world contracts flagged

ChainSecurity stated on Friday that it had discovered 13 cases of potentially exposed real-world contracts and was engaging in responsible disclosure with the projects concerned. While the firm did not reveal the affected projects or details of the discovered cases, it advised developers to assess their contracts urgently. Unlike traditional software, deployed Ethereum contracts cannot simply be patched, which is why the burden of review falls on each project ahead of any new activation date.

The news made a strong impact on community members. Pseudonymous developer pcaversaccio commented on GitHub on October 21 that the situation was “serious” and that the fork must be re-evaluated.

The announcement also comes in the wake of a previous warning from the Ethereum Foundation that Glamsterdam's new gas pricing mechanism could affect wallets, indexers, and gas estimators operating under fixed assumptions.

Glamsterdam launched on the Sepolia testnet on October 6, and Hoodi had been the next expected checkpoint before a mainnet launch — under Ethereum's rollout process, testnet runs act as gates that an upgrade must pass before mainnet. Initially, the team planned a December mainnet deployment, contingent on successful testing of the Hoodi testnet. However, with the Hoodi activation no longer a possibility, the proposed December release should not be viewed as a deadline. The indicators to watch from here are whether a replacement epoch is added to the deployment configuration, what the EIP-8037 interaction evaluation turns up, and what emerges from ChainSecurity's responsible-disclosure exchanges with the 13 flagged projects.