Ethereum developers have penciled in October 6, 2026, at 13:53 UTC as the tentative activation window for Glamsterdam on Sepolia, the network’s public testing environment used to validate major protocol upgrades before they reach the main Ethereum blockchain.
The date, agreed upon during a recent All Core Developers Consensus meeting, remains interim rather than locked in, since developers hadn’t yet achieved a fully stable version of Glamsterdam on any private development network when they selected it.
A fresh round of testing, known as Devnet-11, is now scheduled to begin September 14, replacing what was originally expected to be Devnet-10, and its outcome will largely determine whether the October timeline actually holds.
Ethereum Glamsterdam Upgrade Date Remains Tentative
Developers picked Sepolia epoch 351232 during their September 3 gathering as the target activation point, a decision Ethereum protocol researcher Christine D. Kim confirmed translates to October 6 at 13:53 UTC.
It’s been about a week since this post went out to my Substack subscribers, and the caveats about the Oct 6 Sepolia testnet upgrade date still hold.
The only minor update now is that all eyes are on the launch of Glam-Devnet-11 next Monday, not Devnet-10.
— Christine D. Kim (@christine_dkim) September 10, 2026
Setting that specific epoch gives client development teams, infrastructure operators, and application builders a shared reference point to plan around, but it doesn’t guarantee the fork actually happens on schedule. Developers retain full flexibility to push the date back if upcoming tests surface a grim defect or if client teams can’t ready stable software releases in time.
That caution carries extra weight given that Devnet-9, an former private test network built with roughly 1,000 validator nodes, ran into finality issues, meaning the network struggled to get enough validators aligned on the blockchain’s current state, a problem that can stem from client software bugs, validator behavior, network setup, or startling interactions between different protocol changes bundled into the upgrade.
Devnet-11 Will Test Fixes Before Sepolia
Testing plans have since shifted forward rather than sticking with the originally planned Devnet-10, developers are now directing their attention toward Devnet-11, set to go live Monday, September 14, according to Kim’s latest update shared on social platform X.
An efficiently running Devnet-11 would give Ethereum’s various client teams, the independent software implementations that keep the network running, a reliable environment to test Glamsterdam’s full set of proposed changes together.
This matters because Ethereum trusts on multiple, separately built execution and consensus clients working in harmony, and a bug isolated to just one implementation can still disrupt an entire test network if enough validators are running that particular client.
Particularly, infrastructure players including Lido and Optimism have precisely requested at least one full day of stable network performance before greenlighting the Sepolia fork, underscoring how much weight the industry places on getting this testing phase right before moving forward.
Consensus & EIP-8037 Bugs Extended Testing
Earlier testing rounds surfaced technical problems spanning both core layers of Ethereum’s architecture. On the consensus side, Ethereum Foundation engineer Stefan Starflinger identified an issue during Devnet-8 involving blocks that repeated a parent hash, a bug serious enough that it could have brought the entire test network to a standstill if left unresolved.
Devnet-9 followed with its own finality complications, pushing engineers to dig deeper into more unusual scenarios across a larger set of validators. On the execution side, Ethereum Foundation researcher Maria Silva highlighted a separate implementation problem tied to EIP-8037, a proposal designed to restructure how gas fees are calculated when new blockchain state gets created, covering things like new accounts, smart contracts, and storage entries.
The proposal introduces a multidimensional gas pricing model aimed at controlling network growth as Ethereum’s block gas limits continue rising, though it’s still undergoing peer review. Fixing the bug required execution client teams to revise their code and refine the underlying specification, strengthening the idea that testing exists not just to validate individual proposals but to confirm the entire bundle of changes works smoothly together across different clients and network conditions.
Hoodi & Mainnet Dates Depend On Test Results
Beyond Sepolia, developers have knowingly avoided setting a date for Hoodi, Ethereum’s secondary public testnet that’s expected to mirror mainnet conditions more closely and give staking providers a more realistic testing ground.
Teku client developer Enrico del Fante argued in favor of holding off on a Hoodi date, pointing to the recent Devnet-9 setbacks as reason enough to allow more breathing room following the Sepolia decision.
As for Ethereum’s actual mainnet, a December 2026 activation has come up in developer discussions as a possibility, though it remains nothing more than a lightly discussed target rather than a confirmed date. Scheduling Sepolia for early October does leave enough runway on the calendar for a second public testnet phase and client software preparation, assuming testing continues to progress without major setbacks.
For now, no mainnet epoch, activation timestamp, or confirmed client release schedule has been published, leaving the September 14 Devnet-11 launch as the next concrete milestone developers will be watching closely before deciding whether October 6 remains a genuine target for Sepolia.
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