Ethereum’s development community has officially confirmed the upcoming dates for the much‑anticipated Glamsterdam event, a gathering that brings together core developers, researchers, and ecosystem partners to discuss the future of the blockchain. While the announcement has been welcomed as a sign of steady progress, the Ethereum team also issued a stark warning: the presence of so‑called “fake” builders could pose a serious risk to network performance and security.
The term “fake builders” refers to entities that exploit the test‑net environment by using free test ether to gain an unfair advantage over legitimate participants. In the context of Ethereum’s upcoming test‑net, Sepolia, these malicious actors can bid higher than honest builders for block construction slots, effectively crowding out genuine contributors.
By doing so, they can withhold transaction payloads, delay the inclusion of critical updates, and potentially introduce vulnerabilities that would be difficult to detect in a live environment. To understand why this matters, it is helpful to review how Ethereum’s block‑building process works.
In the proof‑of‑stake (PoS) model, validators are responsible for proposing and attesting to blocks. Builders, often operating as specialized services, package transactions into a payload and then submit that payload to validators for inclusion. When builders compete for the right to have their payloads selected, they typically do so by offering a portion of the transaction fees (known as the “builder fee”) to the validator. The highest‑paying builder wins the slot.
On a test‑net like Sepolia, free test ether is distributed to participants to simulate real‑world conditions without financial risk. However, because the test ether has no intrinsic value, malicious builders can generate large quantities at minimal cost, allowing them to outbid honest participants who are limited by the amount of test ether they receive. The Ethereum team’s warning highlights two primary concerns.
First, the ability of fake builders to outbid honest competitors can distort the natural market dynamics that the test‑net is meant to emulate. This distortion can lead to inaccurate data about fee markets, block times, and network throughput, ultimately compromising the validity of any research or testing conducted during the Glamsterdam sessions. Second, by withholding transaction payloads, these builders can create artificial bottlenecks.
When a validator receives an incomplete or delayed payload, it may be forced to skip a slot or revert to a fallback mechanism, both of which can reduce overall network efficiency and obscure the true performance characteristics of upcoming protocol upgrades. In response to these risks, Ethereum’s client development teams have taken proactive steps to mitigate the impact of fake builders. One notable measure is the reduction of the review window for client submissions ahead of Sepolia’s launch.
Historically, client teams have been given a full review period—often several weeks—to audit code changes, run extensive test suites, and coordinate with other teams. For the upcoming rollout, the review window has been cut to roughly half that time. This accelerated timeline forces developers to prioritize critical security checks and performance evaluations, thereby limiting the window of opportunity for malicious actors to exploit the test‑net. Additionally, the Ethereum Foundation is implementing stricter monitoring of test‑ether distribution.
By tracking the allocation of test ether to individual addresses and correlating that data with builder activity, the foundation hopes to identify patterns indicative of abuse. Addresses that exhibit unusually high bidding behavior relative to their test‑ether balance may be flagged for further investigation, and their ability to submit payloads could be temporarily suspended. Beyond technical safeguards, the community is being urged to adopt best practices when participating in Glamsterdam and the Sepolia test‑net. Builders are encouraged to disclose their fee structures openly, allowing validators to make informed decisions based on transparency rather than solely on the highest bid.
Validators, in turn, are asked to verify the provenance of payloads and to reject any that appear to be intentionally delayed or incomplete. By fostering a culture of openness and mutual accountability, the Ethereum ecosystem can reduce the incentive for malicious behavior. The broader implications of this warning extend to the future of Ethereum’s scaling roadmap. As the network continues to evolve with upgrades such as Danksharding and Proto‑Danksharding, the role of builders becomes increasingly central.
Ensuring that the builder market operates fairly on test‑nets is essential for gaining confidence that it will function correctly on mainnet. Any systemic issues uncovered during Glamsterdam could inform adjustments to the builder‑validator incentive model, potentially leading to new mechanisms that discourage collusion and reward honest participation. In summary, while the confirmation of Glamsterdam dates signals a forward‑moving momentum for Ethereum’s development, the accompanying caution about fake builders serves as a reminder that security and fairness remain paramount. By limiting the review period for client teams, tightening test‑ether monitoring, and promoting transparent builder practices, the Ethereum community aims to safeguard the integrity of its test‑net environment.
These steps are intended to ensure that the data and insights gathered during Glamsterdam accurately reflect the network’s capabilities, ultimately supporting a smoother transition to Sepolia and, eventually, to the next generation of Ethereum mainnet upgrades. Stakeholders, developers, and enthusiasts are encouraged to stay vigilant, report suspicious activity, and contribute to the collective effort of maintaining a robust, resilient blockchain. The success of Glamsterdam—and the health of Ethereum’s broader ecosystem—depends on the collaborative commitment of all participants to uphold the principles of openness, security, and fairness.