Ethereum developers have delayed the Glamsterdam upgrade on the Hoodi testnet after security auditors found that its proposed gas changes could break existing smart contracts.

The Ethereum Foundation said in a blog post on 6 November that auditing firm ChainSecurity had identified several projects that could become vulnerable once the upgrade's EIP-8037 and EIP-8038 take effect. The two proposals change how Ethereum charges gas for certain operations, particularly the creation of and access to blockchain state.

Some existing contracts assume certain operations will cost a fixed amount of gas, or that a failed operation will leave too little gas for later instructions. Glamsterdam's revised accounting could invalidate those assumptions, letting operations finish when developers expected the whole transaction to revert.

Eight broken invariants found

ChainSecurity detailed the concerns in a 13 October analysis, identifying eight smart contract assumptions — known as invariants — that the new gas model could break. The Ethereum Foundation has published a GitHub repository documenting the eight affected invariants, with explanations, examples and instructions for developers to check their code.

Ethereum's All Core Developers group has therefore decided to hold off on the Hoodi hard fork until the concerns are resolved. The Hoodi activation had originally been scheduled for 26 October, alongside a planned increase in the testnet's gas limit to 200 million. No replacement date has been announced.

The Foundation said it is working with ChainSecurity and Dedaub, alongside internal audits, to assess the effects across existing applications, and has asked developers and auditors to report vulnerable contracts. Work on Ethereum's subsequent Hegota upgrade will continue in parallel and is unaffected. Glamsterdam had already activated on the Sepolia testnet on 6 October.

Ether fell about 6 per cent to around $2,220 on Friday as the delay coincided with a broad sell-off in cryptocurrencies.