Ethereum developers have tentatively scheduled the Glamsterdam upgrade for the Sepolia testnet on October 6. However, this date is conditional on the successful completion of ongoing testing phases, which have uncovered several bugs and issues, casting uncertainty over the upgrade’s readiness and its subsequent mainnet activation targeted for December 2026.
The tentative October 6 date for the Sepolia testnet was agreed upon by developers, as noted by protocol specialist Christine D. Kim. This timeline hinges on the next testing phase producing a stable network, as Glamsterdam has yet to run successfully on a stable private devnet. This inherent uncertainty extends to the broader roadmap, with the mainnet release still targeted for December 2026 but not guaranteed.
Testing Challenges and Bug Discoveries
Recent testing has highlighted significant challenges. Glamsterdam-Devnet-9, launched on September 1 with 1,000 validator nodes, revealed issues with network finalization, meaning too few validators are correctly proposing and attesting to the chain head. Ethereum Foundation (EF) developer operations engineer Stefan Starflinger stated that the network’s size exposed “quite a few edge cases and issues” that require addressing. He also mentioned that Devnet-8 encountered a more severe bug that could freeze the entire network if a validator proposed a block sharing its parent’s hash.
Further complicating the testing process, EF researcher Maria Silva flagged a bug related to EIP-8037, the State Creation Gas Cost Increase, which necessitates updates to execution-layer client code. Due to these fixes, the next devnet to monitor is Devnet-11, not Devnet-10 as initially planned. Parithosh Jayanti, an EF developer operations engineer, indicated that if Devnet-11 also fails, the October 6 date would need to be re-evaluated on a case-by-case basis.
Impact on Future Timelines and Roadmaps
Concerns about the current testing environment have also influenced plans for subsequent testnets. Enrico del Fante of Consensys suggested delaying the commitment to Hoodi, Ethereum’s second public testnet, by a few weeks due to the problems found on Devnet-9. This cautious approach underscores the iterative nature of the development process.
The uncertainty surrounding the testnet phases directly impacts confidence in the mainnet release timeline. While developers aim for a December 2026 mainnet activation for Glamsterdam, the ongoing technical hurdles and the current readiness of client implementations mean this date is not assured. This development follows a pattern of Ethereum shipping major changes approximately twice a year, as seen with the Fusaka upgrade’s activation last December.
The broader Ethereum roadmap includes the Hegotá upgrade following Glamsterdam, and a future push toward quantum-resistant infrastructure targeted for 2029. However, the immediate focus remains on successfully navigating the testing and deployment of Glamsterdam, with the Sepolia testnet date serving as a critical, albeit tentative, milestone.
Why This Matters
The materials describe a narrow update: Ethereum developers have set a tentative date of October 6 for the Glamsterdam upgrade on the Sepolia testnet, contingent on successful testing. Whether the next testing phase can produce a stable network for the Glamsterdam upgrade.
Broader Context
Source materials place the factual news in this context: Ethereum developers have tentatively scheduled the Glamsterdam upgrade for Ethereum’s Sepolia testnet on October 6 at 13:53 UTC, even as private devnet testing continues to uncover bugs.









