Ethereum’s Sepolia testnet is scheduled to activate the Glamsterdam upgrade on October 6, 2026, marking an important milestone in the development of Ethereum’s next major protocol update.
The activation is scheduled for 13:53:36 UTC at epoch 353,024 and slot 11,296,768. The fixed activation point gives Ethereum developers a defined environment in which to test Glamsterdam before the upgrade moves further through the deployment process.
Glamsterdam remains in testing, with Ethereum’s development roadmap targeting a mainnet release during the fourth quarter of 2026. No final mainnet activation date has been set.
Sepolia Becomes the Next Major Testing Ground
The Sepolia activation will allow developers to examine Glamsterdam under live testnet conditions.
One of the central components of the upgrade is enshrined proposer-builder separation, commonly known as ePBS. The proposed system changes how Ethereum handles the relationship between validators that propose blocks and builders responsible for assembling the execution portion of those blocks.
Testing the system on Sepolia will allow developers to identify technical problems and assess how the new mechanisms behave before they are considered for deployment on Ethereum’s main network.
Free Testnet ETH Creates a Testing Challenge
Developers have identified a potential problem with Glamsterdam testing on Sepolia.
Because Sepolia ETH is freely available and builder identities can be replaced relatively easily, an attacker could potentially create new identities, repeatedly participate in block-building auctions and then fail to deliver the transaction payloads associated with winning bids.
Under normal economic conditions, repeatedly making unsuccessful or disruptive bids would carry a cost. On a testnet where the native asset has no real-world value, that financial barrier is much lower.
Such behaviour could interfere with testing by repeatedly disrupting the auction and payload-delivery process.
The issue is limited to the testnet environment. It does not put funds on Ethereum’s mainnet at risk.
Testing Payload Delivery Under ePBS
The ePBS design is closely connected to how builders commit to and deliver execution payloads.
Under the proposed system, a builder can commit to an execution payload and reveal it later. Additional mechanisms are designed to monitor whether the winning builder delivers the payload within the required timeframe.
This makes payload delivery an important part of Glamsterdam’s testing.
On Sepolia, developers will be able to observe how the system behaves if a winning builder fails to provide its promised payload. The availability of inexpensive testnet ETH and easily replaceable identities could make repeated testing of this scenario possible.
While such activity could complicate or slow development work, it does not create a comparable financial threat to Ethereum’s mainnet.
Hoodi and Mainnet Dates Remain Unconfirmed
The Ethereum development process includes multiple testnets before a major upgrade can be deployed on mainnet.
During a September 17 All Core Developers consensus meeting, October 6 was recorded for the Sepolia activation, while October 27 was discussed as a tentative date for the Hoodi testnet.
A mainnet activation date was not established.
The October 6 Sepolia milestone therefore represents the next confirmed stage in Glamsterdam’s rollout.
Developers will use the testnet deployment to evaluate the upgrade’s scaling-related changes, including ePBS and the mechanisms intended to ensure timely delivery of execution payloads.
What Comes Next for Glamsterdam
Glamsterdam is expected to introduce several changes aimed at improving Ethereum’s ability to scale while refining the way blocks are built and proposed.
However, the upgrade remains under development and testing. A successful Sepolia activation will not automatically guarantee a mainnet launch on a particular date.
The results from Sepolia, followed by testing on other networks such as Hoodi, will help developers determine whether the upgrade is ready for the next stage.
For now, October 6 is the key date to watch. It will give Ethereum developers their first major public test of Glamsterdam’s new architecture and provide further information about how the proposed changes perform under real testnet conditions.
Disclaimer: This article is for informational purposes only and does not constitute legal, tax, investment, financial or other professional advice.
